<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:ce98f756-8ae9-470c-8ed3-b7fa2007976b,g:20c9d306-794a-49ca-974c-afb8663cbec6-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://prth.com/role/UnauditedConsolidatedStatementsofChangesinStockholdersDeficitandNonControllingInterest" xlink:type="simple" xlink:href="prth-20250630.xsd#UnauditedConsolidatedStatementsofChangesinStockholdersDeficitandNonControllingInterest"/>
  <link:definitionLink xlink:role="http://prth.com/role/UnauditedConsolidatedStatementsofChangesinStockholdersDeficitandNonControllingInterest" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_138ad90d-cdec-4545-abbe-8cab348353f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_a1e431c1-3bce-4cea-a999-47d817e7c36c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_138ad90d-cdec-4545-abbe-8cab348353f7" xlink:to="loc_us-gaap_StatementTable_a1e431c1-3bce-4cea-a999-47d817e7c36c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_1e790378-6e31-499e-b9a2-586788853e1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_a1e431c1-3bce-4cea-a999-47d817e7c36c" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_1e790378-6e31-499e-b9a2-586788853e1b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_1e790378-6e31-499e-b9a2-586788853e1b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_1e790378-6e31-499e-b9a2-586788853e1b" xlink:to="loc_us-gaap_EquityComponentDomain_1e790378-6e31-499e-b9a2-586788853e1b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_33035fef-da8a-440f-9e5d-0846df5a1950" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_1e790378-6e31-499e-b9a2-586788853e1b" xlink:to="loc_us-gaap_EquityComponentDomain_33035fef-da8a-440f-9e5d-0846df5a1950" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ParentMember_d3f7c489-51ed-4919-9fe9-c72f4bcc1130" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_33035fef-da8a-440f-9e5d-0846df5a1950" xlink:to="loc_us-gaap_ParentMember_d3f7c489-51ed-4919-9fe9-c72f4bcc1130" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_7f80e339-3349-40ef-beb0-de661702ea55" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_d3f7c489-51ed-4919-9fe9-c72f4bcc1130" xlink:to="loc_us-gaap_CommonStockMember_7f80e339-3349-40ef-beb0-de661702ea55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_53847818-a8b4-452a-9b02-e69791228c97" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_d3f7c489-51ed-4919-9fe9-c72f4bcc1130" xlink:to="loc_us-gaap_TreasuryStockCommonMember_53847818-a8b4-452a-9b02-e69791228c97" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_a4d3c5fd-43f1-484b-9d8b-b86e430ac090" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_d3f7c489-51ed-4919-9fe9-c72f4bcc1130" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_a4d3c5fd-43f1-484b-9d8b-b86e430ac090" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_17c630f8-21e2-4cfe-a41d-d2284815b0f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_d3f7c489-51ed-4919-9fe9-c72f4bcc1130" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_17c630f8-21e2-4cfe-a41d-d2284815b0f5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_1d2bb152-ec3d-4958-adec-64406dc06749" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ParentMember_d3f7c489-51ed-4919-9fe9-c72f4bcc1130" xlink:to="loc_us-gaap_RetainedEarningsMember_1d2bb152-ec3d-4958-adec-64406dc06749" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestMember_d8787852-0f95-4e39-861f-c9cae025dfd9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_33035fef-da8a-440f-9e5d-0846df5a1950" xlink:to="loc_us-gaap_NoncontrollingInterestMember_d8787852-0f95-4e39-861f-c9cae025dfd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_138ad90d-cdec-4545-abbe-8cab348353f7" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_49869b20-780b-4aa0-aaff-74f28bfe347e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_49869b20-780b-4aa0-aaff-74f28bfe347e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_c707db55-710f-4832-b7c1-1184bd048f1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_TreasuryStockCommonShares_c707db55-710f-4832-b7c1-1184bd048f1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_09d02e12-3f99-4aaa-84f7-0e61c483a076" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_09d02e12-3f99-4aaa-84f7-0e61c483a076" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationOtherLongtermIncentivePlansRequisiteServicePeriodRecognition_279b8134-06a4-4c24-90a3-0cd477b393ac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationOtherLongtermIncentivePlansRequisiteServicePeriodRecognition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationOtherLongtermIncentivePlansRequisiteServicePeriodRecognition_279b8134-06a4-4c24-90a3-0cd477b393ac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_59817f21-f6ed-48c4-81f9-9f635ca9c0fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensation_59817f21-f6ed-48c4-81f9-9f635ca9c0fc" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_13e1e2a6-e9c0-497c-a7b3-550bfbcb4215" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation_13e1e2a6-e9c0-497c-a7b3-550bfbcb4215" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_be6e8a3f-c0c4-4f5a-8463-443d1f76ff28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_be6e8a3f-c0c4-4f5a-8463-443d1f76ff28" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_72def905-7de7-4e90-98d4-432cec62ce0d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_72def905-7de7-4e90-98d4-432cec62ce0d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_AdjustmentsToAdditionalPaidInCapitalRedemptionOfRedeemableNoncontrollingInterest_16f474c5-f524-4735-a410-c324b1061ffb" xlink:href="prth-20250630.xsd#prth_AdjustmentsToAdditionalPaidInCapitalRedemptionOfRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_prth_AdjustmentsToAdditionalPaidInCapitalRedemptionOfRedeemableNoncontrollingInterest_16f474c5-f524-4735-a410-c324b1061ffb" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_AdjustmentsToAdditionalPaidInCapitalDecreaseFromReturnOnRedeemableNoncontrollingInterest_7c24a18a-0b61-4572-8d0f-0f1a508ac793" xlink:href="prth-20250630.xsd#prth_AdjustmentsToAdditionalPaidInCapitalDecreaseFromReturnOnRedeemableNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_prth_AdjustmentsToAdditionalPaidInCapitalDecreaseFromReturnOnRedeemableNoncontrollingInterest_7c24a18a-0b61-4572-8d0f-0f1a508ac793" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_5813339b-2b6a-4713-be6d-ee11f9e4db35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_5813339b-2b6a-4713-be6d-ee11f9e4db35" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_f9fded2f-fee9-4afe-94b8-09c57b3e4774" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_f9fded2f-fee9-4afe-94b8-09c57b3e4774" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_88eb6fea-6c43-4a75-947a-cf905a8c324b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities_88eb6fea-6c43-4a75-947a-cf905a8c324b" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_192e18a3-65f1-4113-b8f2-1da13df9828e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_192e18a3-65f1-4113-b8f2-1da13df9828e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings_ed9be490-4518-493f-b8c5-4f34ffc2afad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings_ed9be490-4518-493f-b8c5-4f34ffc2afad" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_AdjustmentsToAdditionalPaidInCapitalAccretionOfTemporaryEquityDiscount_4ef5069b-9ee4-4eba-8684-b112fd53910f" xlink:href="prth-20250630.xsd#prth_AdjustmentsToAdditionalPaidInCapitalAccretionOfTemporaryEquityDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_prth_AdjustmentsToAdditionalPaidInCapitalAccretionOfTemporaryEquityDiscount_4ef5069b-9ee4-4eba-8684-b112fd53910f" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_8c57c1fb-514e-4d51-af60-f508b78a2a79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_8c57c1fb-514e-4d51-af60-f508b78a2a79" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_aa7d7a1d-7494-4ce9-861b-f7ff7819995e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_aa7d7a1d-7494-4ce9-861b-f7ff7819995e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_AdditionalPaidInCapitalIncreaseForReclassificationOfDeficit_ad2ccc33-e192-4665-a084-21dc5be24f25" xlink:href="prth-20250630.xsd#prth_AdditionalPaidInCapitalIncreaseForReclassificationOfDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_prth_AdditionalPaidInCapitalIncreaseForReclassificationOfDeficit_ad2ccc33-e192-4665-a084-21dc5be24f25" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProfitLoss_32c81e69-828a-4ffa-9cef-e9f40d88b4af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfitLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_e40fb67a-9815-4750-8ef5-9194bf95b3be" xlink:to="loc_us-gaap_ProfitLoss_32c81e69-828a-4ffa-9cef-e9f40d88b4af" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_2de51053-6159-40f5-9537-77e0da667e21" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_ca3cbadf-5d3a-4522-9311-2e61bf3f4298" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_42e2f344-3e54-4f7a-8018-51a65a892f5e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/BasisofPresentationandSignificantAccountingPoliciesScheduleofAllowanceforTradeReceivablesandSettlementAssetsDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#BasisofPresentationandSignificantAccountingPoliciesScheduleofAllowanceforTradeReceivablesandSettlementAssetsDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/BasisofPresentationandSignificantAccountingPoliciesScheduleofAllowanceforTradeReceivablesandSettlementAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_c7ac80fe-be91-4ece-9ca2-7c3a2e7db80b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_c01ec713-2758-4cac-9760-323300e0bba3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_c7ac80fe-be91-4ece-9ca2-7c3a2e7db80b" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_c01ec713-2758-4cac-9760-323300e0bba3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_55f11455-48d8-4938-acd0-19f93d95b259" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_c01ec713-2758-4cac-9760-323300e0bba3" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_55f11455-48d8-4938-acd0-19f93d95b259" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_55f11455-48d8-4938-acd0-19f93d95b259_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_55f11455-48d8-4938-acd0-19f93d95b259" xlink:to="loc_us-gaap_ReceivableTypeDomain_55f11455-48d8-4938-acd0-19f93d95b259_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_e7bbdbcc-bdd7-4ac2-86f2-bc98df7b8430" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_55f11455-48d8-4938-acd0-19f93d95b259" xlink:to="loc_us-gaap_ReceivableTypeDomain_e7bbdbcc-bdd7-4ac2-86f2-bc98df7b8430" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeAccountsReceivableMember_ae089ab1-c7d9-4de7-a8f4-7a47f45ef33f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeAccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_e7bbdbcc-bdd7-4ac2-86f2-bc98df7b8430" xlink:to="loc_us-gaap_TradeAccountsReceivableMember_ae089ab1-c7d9-4de7-a8f4-7a47f45ef33f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_SettlementAssetsMember_ac0b43d5-bbab-446d-aa04-7dc28d321278" xlink:href="prth-20250630.xsd#prth_SettlementAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_e7bbdbcc-bdd7-4ac2-86f2-bc98df7b8430" xlink:to="loc_prth_SettlementAssetsMember_ac0b43d5-bbab-446d-aa04-7dc28d321278" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_19611b00-19ef-46ff-a3f2-e4e2636c1ad0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_c7ac80fe-be91-4ece-9ca2-7c3a2e7db80b" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_19611b00-19ef-46ff-a3f2-e4e2636c1ad0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_0c72ce13-cd54-418d-a9c9-a7a01e0eea93" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_19611b00-19ef-46ff-a3f2-e4e2636c1ad0" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_0c72ce13-cd54-418d-a9c9-a7a01e0eea93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_AccountsReceivableAllowanceForCreditLossWriteoffRecovery_8929b3ae-e405-438f-b0b6-74da2e2e14bd" xlink:href="prth-20250630.xsd#prth_AccountsReceivableAllowanceForCreditLossWriteoffRecovery"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_19611b00-19ef-46ff-a3f2-e4e2636c1ad0" xlink:to="loc_prth_AccountsReceivableAllowanceForCreditLossWriteoffRecovery_8929b3ae-e405-438f-b0b6-74da2e2e14bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProvisionForDoubtfulAccounts_84a17a54-f6a2-46a4-b5f0-cbde82f465ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProvisionForDoubtfulAccounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_19611b00-19ef-46ff-a3f2-e4e2636c1ad0" xlink:to="loc_us-gaap_ProvisionForDoubtfulAccounts_84a17a54-f6a2-46a4-b5f0-cbde82f465ae" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_AccountsReceivableAllowanceForCreditLossReclassification_1beeeb76-cb87-4eb7-b1c3-2385c8f2acee" xlink:href="prth-20250630.xsd#prth_AccountsReceivableAllowanceForCreditLossReclassification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableRollforward_19611b00-19ef-46ff-a3f2-e4e2636c1ad0" xlink:to="loc_prth_AccountsReceivableAllowanceForCreditLossReclassification_1beeeb76-cb87-4eb7-b1c3-2385c8f2acee" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_eaf9acb2-0754-41ba-ad02-9468850f7aae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/AcquisitionNarrativeDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#AcquisitionNarrativeDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/AcquisitionNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_2727c6cb-d1a3-40a5-87f4-9ff114357b3f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_2727c6cb-d1a3-40a5-87f4-9ff114357b3f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_ed5af7f3-3a8c-45cf-942b-0f4990d99991" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_2727c6cb-d1a3-40a5-87f4-9ff114357b3f" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_ed5af7f3-3a8c-45cf-942b-0f4990d99991" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_ed5af7f3-3a8c-45cf-942b-0f4990d99991_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_ed5af7f3-3a8c-45cf-942b-0f4990d99991" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_ed5af7f3-3a8c-45cf-942b-0f4990d99991_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_dd11a41d-1895-4918-9df3-2cae141aaaf9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_ed5af7f3-3a8c-45cf-942b-0f4990d99991" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_dd11a41d-1895-4918-9df3-2cae141aaaf9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_LetusBusinessMember_15526bcd-68a5-4bbe-87a1-7ecca1a979d0" xlink:href="prth-20250630.xsd#prth_LetusBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_dd11a41d-1895-4918-9df3-2cae141aaaf9" xlink:to="loc_prth_LetusBusinessMember_15526bcd-68a5-4bbe-87a1-7ecca1a979d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_1f8656c1-cd93-4f10-b505-32207f4d0937" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_1f8656c1-cd93-4f10-b505-32207f4d0937" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_8a5ea6f9-b0d1-4e1a-b154-7f3f7e5c7313" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_8a5ea6f9-b0d1-4e1a-b154-7f3f7e5c7313" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_fd92fdb6-2a76-4a71-aa9e-d0c1b18370b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_fd92fdb6-2a76-4a71-aa9e-d0c1b18370b1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_1fca7669-44ad-492d-8fac-f61ed627f3fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_1fca7669-44ad-492d-8fac-f61ed627f3fa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_BusinessCombinationConsiderationTransferredContingentConsideration_5ba1da8c-1064-4e70-8b95-8ecfb246eddc" xlink:href="prth-20250630.xsd#prth_BusinessCombinationConsiderationTransferredContingentConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_prth_BusinessCombinationConsiderationTransferredContingentConsideration_5ba1da8c-1064-4e70-8b95-8ecfb246eddc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_BusinessCombinationDeferredConsiderationLiability_f1355e4d-62b1-47bd-8830-855f43f576c2" xlink:href="prth-20250630.xsd#prth_BusinessCombinationDeferredConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_prth_BusinessCombinationDeferredConsiderationLiability_f1355e4d-62b1-47bd-8830-855f43f576c2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_BusinessCombinationContingentConsiderationPaymentsPercentageThreshold_c6c4f2d3-20ec-417c-8042-0f52529a1aea" xlink:href="prth-20250630.xsd#prth_BusinessCombinationContingentConsiderationPaymentsPercentageThreshold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_prth_BusinessCombinationContingentConsiderationPaymentsPercentageThreshold_c6c4f2d3-20ec-417c-8042-0f52529a1aea" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_BusinessCombinationContingentConsiderationInterestAccreted_6e3caec3-0a56-4718-b02e-b552bb56268d" xlink:href="prth-20250630.xsd#prth_BusinessCombinationContingentConsiderationInterestAccreted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_prth_BusinessCombinationContingentConsiderationInterestAccreted_6e3caec3-0a56-4718-b02e-b552bb56268d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_BusinessCombinationDeferredConsiderationLiabilityCurrent_aa9f6dc0-19b4-440c-a39c-4e0a985e7734" xlink:href="prth-20250630.xsd#prth_BusinessCombinationDeferredConsiderationLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_prth_BusinessCombinationDeferredConsiderationLiabilityCurrent_aa9f6dc0-19b4-440c-a39c-4e0a985e7734" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_BusinessCombinationDeferredConsiderationLiabilityNoncurrent_5c3b33d5-fd1f-4c33-9f4c-eb21a54fbc09" xlink:href="prth-20250630.xsd#prth_BusinessCombinationDeferredConsiderationLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_prth_BusinessCombinationDeferredConsiderationLiabilityNoncurrent_5c3b33d5-fd1f-4c33-9f4c-eb21a54fbc09" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_4c3742bc-a75b-4228-9502-2a9019a1ffd4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_4c3742bc-a75b-4228-9502-2a9019a1ffd4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_47f05b56-246c-416b-900c-296e8f450f59" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_us-gaap_NetIncomeLoss_47f05b56-246c-416b-900c-296e8f450f59" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_40f25431-571e-4d73-9e1e-084b86684840" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_8bc054fc-7144-451b-aeda-c3932ea40adb" xlink:to="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_40f25431-571e-4d73-9e1e-084b86684840" xlink:type="arc" order="12"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/AcquisitionPurchasePriceAllocationDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#AcquisitionPurchasePriceAllocationDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/AcquisitionPurchasePriceAllocationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_0283a92c-e377-41f0-a790-b92c45f0b943" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e2cfce1f-dbb8-4bc3-ab52-bc814c687f25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0283a92c-e377-41f0-a790-b92c45f0b943" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e2cfce1f-dbb8-4bc3-ab52-bc814c687f25" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_e8f1bbdf-31f1-4c10-a703-7d3641cf37ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e2cfce1f-dbb8-4bc3-ab52-bc814c687f25" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_e8f1bbdf-31f1-4c10-a703-7d3641cf37ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e8f1bbdf-31f1-4c10-a703-7d3641cf37ea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_e8f1bbdf-31f1-4c10-a703-7d3641cf37ea" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_e8f1bbdf-31f1-4c10-a703-7d3641cf37ea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_84ff127e-3cda-4657-ba7d-9a225572074b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_e8f1bbdf-31f1-4c10-a703-7d3641cf37ea" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_84ff127e-3cda-4657-ba7d-9a225572074b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_LetusBusinessMember_4a7f6b36-e14d-4841-890b-4f66d9dd8c7d" xlink:href="prth-20250630.xsd#prth_LetusBusinessMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_84ff127e-3cda-4657-ba7d-9a225572074b" xlink:to="loc_prth_LetusBusinessMember_4a7f6b36-e14d-4841-890b-4f66d9dd8c7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_bb2fb012-226e-4cd6-93cd-ae5a5a7f336a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_e2cfce1f-dbb8-4bc3-ab52-bc814c687f25" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_bb2fb012-226e-4cd6-93cd-ae5a5a7f336a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bb2fb012-226e-4cd6-93cd-ae5a5a7f336a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_bb2fb012-226e-4cd6-93cd-ae5a5a7f336a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_bb2fb012-226e-4cd6-93cd-ae5a5a7f336a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_53d35f79-3d3e-4512-9adb-7aa9d8f35cce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_bb2fb012-226e-4cd6-93cd-ae5a5a7f336a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_53d35f79-3d3e-4512-9adb-7aa9d8f35cce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_06cf3387-5b6a-4c64-94d8-21e9b0660160" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_53d35f79-3d3e-4512-9adb-7aa9d8f35cce" xlink:to="loc_us-gaap_CustomerRelationshipsMember_06cf3387-5b6a-4c64-94d8-21e9b0660160" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TrademarksMember_6ed76616-cb07-4a86-aa53-3558ac437288" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TrademarksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_53d35f79-3d3e-4512-9adb-7aa9d8f35cce" xlink:to="loc_us-gaap_TrademarksMember_6ed76616-cb07-4a86-aa53-3558ac437288" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_38013482-7821-4fb8-8698-f72001264dd0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_53d35f79-3d3e-4512-9adb-7aa9d8f35cce" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_38013482-7821-4fb8-8698-f72001264dd0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_4ed1e66c-28fe-43ad-9029-dd02c84f2a90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferredAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0283a92c-e377-41f0-a790-b92c45f0b943" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_4ed1e66c-28fe-43ad-9029-dd02c84f2a90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesGross_ab13d6c7-ef82-4542-a1e9-8f2eea710a26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_4ed1e66c-28fe-43ad-9029-dd02c84f2a90" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesGross_ab13d6c7-ef82-4542-a1e9-8f2eea710a26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_c76feccd-fa5b-409e-bbcb-09c5d6f753d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_4ed1e66c-28fe-43ad-9029-dd02c84f2a90" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferredLiabilitiesIncurred_c76feccd-fa5b-409e-bbcb-09c5d6f753d6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_BusinessCombinationConsiderationTransferredContingentConsideration_3fd78db9-db8f-4484-a483-81c36577c559" xlink:href="prth-20250630.xsd#prth_BusinessCombinationConsiderationTransferredContingentConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_4ed1e66c-28fe-43ad-9029-dd02c84f2a90" xlink:to="loc_prth_BusinessCombinationConsiderationTransferredContingentConsideration_3fd78db9-db8f-4484-a483-81c36577c559" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAcquiredFromAcquisition_5ed4aa1f-d385-4fc2-9ba4-2634e33d8e58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAcquiredFromAcquisition"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_4ed1e66c-28fe-43ad-9029-dd02c84f2a90" xlink:to="loc_us-gaap_CashAcquiredFromAcquisition_5ed4aa1f-d385-4fc2-9ba4-2634e33d8e58" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_BusinessCombinationConsiderationTransferredNetOfCashAcquired_bfb49277-8e0c-4259-ba4e-7b92f3783ab2" xlink:href="prth-20250630.xsd#prth_BusinessCombinationConsiderationTransferredNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationConsiderationTransferredAbstract_4ed1e66c-28fe-43ad-9029-dd02c84f2a90" xlink:to="loc_prth_BusinessCombinationConsiderationTransferredNetOfCashAcquired_bfb49277-8e0c-4259-ba4e-7b92f3783ab2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_8a63ecb4-6e34-453c-9633-83b21f015f67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0283a92c-e377-41f0-a790-b92c45f0b943" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_8a63ecb4-6e34-453c-9633-83b21f015f67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_f638421a-dac2-4cc3-9361-e73d43151847" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_8a63ecb4-6e34-453c-9633-83b21f015f67" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsReceivables_f638421a-dac2-4cc3-9361-e73d43151847" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_7419a9c8-4834-4b6d-b1cf-1c546bc8d7e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_8a63ecb4-6e34-453c-9633-83b21f015f67" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssetsPrepaidExpenseAndOtherAssets_7419a9c8-4834-4b6d-b1cf-1c546bc8d7e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedEquipment_809c47f7-f3f2-44dd-b628-40d9d20ddf0f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_8a63ecb4-6e34-453c-9633-83b21f015f67" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedEquipment_809c47f7-f3f2-44dd-b628-40d9d20ddf0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_d7c87d8f-e2bf-46f4-9bcc-959cf02f92ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_8a63ecb4-6e34-453c-9633-83b21f015f67" xlink:to="loc_us-gaap_Goodwill_d7c87d8f-e2bf-46f4-9bcc-959cf02f92ba" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_06c49b87-8df6-4d87-9686-89b7da9b014c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_8a63ecb4-6e34-453c-9633-83b21f015f67" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_06c49b87-8df6-4d87-9686-89b7da9b014c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_d143fd07-263d-49cf-acae-3614f5bdac47" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_8a63ecb4-6e34-453c-9633-83b21f015f67" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilitiesAccountsPayable_d143fd07-263d-49cf-acae-3614f5bdac47" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_4da44a0b-74d9-4ebd-9c47-8503d955e119" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedAssetsAbstract_8a63ecb4-6e34-453c-9633-83b21f015f67" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_4da44a0b-74d9-4ebd-9c47-8503d955e119" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets_667627c9-489c-4068-b197-c2d61b4c3014" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_0283a92c-e377-41f0-a790-b92c45f0b943" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssets_667627c9-489c-4068-b197-c2d61b4c3014" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/RevenuesDisaggregationofRevenuesDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#RevenuesDisaggregationofRevenuesDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/RevenuesDisaggregationofRevenuesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_65aaa223-eca3-4b85-b25e-0685da3589e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_5927ee5c-c18e-4e60-ab09-f0110e6a8fec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_65aaa223-eca3-4b85-b25e-0685da3589e4" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_5927ee5c-c18e-4e60-ab09-f0110e6a8fec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_cb469b07-d282-4e29-8ac7-46ddb5f94f93" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_5927ee5c-c18e-4e60-ab09-f0110e6a8fec" xlink:to="loc_srt_ProductOrServiceAxis_cb469b07-d282-4e29-8ac7-46ddb5f94f93" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_cb469b07-d282-4e29-8ac7-46ddb5f94f93_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_cb469b07-d282-4e29-8ac7-46ddb5f94f93" xlink:to="loc_srt_ProductsAndServicesDomain_cb469b07-d282-4e29-8ac7-46ddb5f94f93_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_d4d1f438-2abc-4eec-80d3-161a2c841f5c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_cb469b07-d282-4e29-8ac7-46ddb5f94f93" xlink:to="loc_srt_ProductsAndServicesDomain_d4d1f438-2abc-4eec-80d3-161a2c841f5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_MerchantCardFeesMember_14ac3900-6945-4da6-92dd-affdc57939f1" xlink:href="prth-20250630.xsd#prth_MerchantCardFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_d4d1f438-2abc-4eec-80d3-161a2c841f5c" xlink:to="loc_prth_MerchantCardFeesMember_14ac3900-6945-4da6-92dd-affdc57939f1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_MoneyTransmissionsServicesMember_d884d5e8-b61f-4a05-8fb0-07d3fcced587" xlink:href="prth-20250630.xsd#prth_MoneyTransmissionsServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_d4d1f438-2abc-4eec-80d3-161a2c841f5c" xlink:to="loc_prth_MoneyTransmissionsServicesMember_d884d5e8-b61f-4a05-8fb0-07d3fcced587" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_OutsourcedServicesAndOtherServicesMember_9c01b61a-7415-4617-8377-b2666a1f5266" xlink:href="prth-20250630.xsd#prth_OutsourcedServicesAndOtherServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_d4d1f438-2abc-4eec-80d3-161a2c841f5c" xlink:to="loc_prth_OutsourcedServicesAndOtherServicesMember_9c01b61a-7415-4617-8377-b2666a1f5266" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_635babdd-a978-4f9d-8e43-89827e8d56bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_d4d1f438-2abc-4eec-80d3-161a2c841f5c" xlink:to="loc_us-gaap_ProductMember_635babdd-a978-4f9d-8e43-89827e8d56bd" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_6ad5d938-3721-4d43-beed-8b18cde8b07b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_5927ee5c-c18e-4e60-ab09-f0110e6a8fec" xlink:to="loc_srt_ConsolidationItemsAxis_6ad5d938-3721-4d43-beed-8b18cde8b07b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_6ad5d938-3721-4d43-beed-8b18cde8b07b_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_6ad5d938-3721-4d43-beed-8b18cde8b07b" xlink:to="loc_srt_ConsolidationItemsDomain_6ad5d938-3721-4d43-beed-8b18cde8b07b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_87061b98-93c1-4022-9365-50b4e68e37f3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_6ad5d938-3721-4d43-beed-8b18cde8b07b" xlink:to="loc_srt_ConsolidationItemsDomain_87061b98-93c1-4022-9365-50b4e68e37f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_f16e8e9f-1853-468c-87c5-0515bcaa1fed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_87061b98-93c1-4022-9365-50b4e68e37f3" xlink:to="loc_us-gaap_OperatingSegmentsMember_f16e8e9f-1853-468c-87c5-0515bcaa1fed" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_b85c77e5-8c22-4b8c-a4d2-89235866df90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_87061b98-93c1-4022-9365-50b4e68e37f3" xlink:to="loc_us-gaap_IntersegmentEliminationMember_b85c77e5-8c22-4b8c-a4d2-89235866df90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_08ca4af2-e3d0-4f59-861e-1756096a96ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_5927ee5c-c18e-4e60-ab09-f0110e6a8fec" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_08ca4af2-e3d0-4f59-861e-1756096a96ef" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_08ca4af2-e3d0-4f59-861e-1756096a96ef_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_08ca4af2-e3d0-4f59-861e-1756096a96ef" xlink:to="loc_us-gaap_SegmentDomain_08ca4af2-e3d0-4f59-861e-1756096a96ef_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_3d946fb6-e48d-4490-bfbc-890748274b79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_08ca4af2-e3d0-4f59-861e-1756096a96ef" xlink:to="loc_us-gaap_SegmentDomain_3d946fb6-e48d-4490-bfbc-890748274b79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_SMBPaymentsSegmentMember_e2dab2a4-0929-4271-bae5-d04bddd2d22c" xlink:href="prth-20250630.xsd#prth_SMBPaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_3d946fb6-e48d-4490-bfbc-890748274b79" xlink:to="loc_prth_SMBPaymentsSegmentMember_e2dab2a4-0929-4271-bae5-d04bddd2d22c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_B2BPaymentsSegmentMember_10d897b3-80f6-4e30-90de-78ee965d5bee" xlink:href="prth-20250630.xsd#prth_B2BPaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_3d946fb6-e48d-4490-bfbc-890748274b79" xlink:to="loc_prth_B2BPaymentsSegmentMember_10d897b3-80f6-4e30-90de-78ee965d5bee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_EnterprisePaymentsSegmentMember_34b1a7e4-f50d-4f2c-bd4b-ec149dc7928f" xlink:href="prth-20250630.xsd#prth_EnterprisePaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_3d946fb6-e48d-4490-bfbc-890748274b79" xlink:to="loc_prth_EnterprisePaymentsSegmentMember_34b1a7e4-f50d-4f2c-bd4b-ec149dc7928f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_2d7eea54-d07e-4a3d-81e6-c43a4a3e5e68" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_65aaa223-eca3-4b85-b25e-0685da3589e4" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_2d7eea54-d07e-4a3d-81e6-c43a4a3e5e68" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeOperating_be7d457f-5a37-4dff-9967-6a04edecc69b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestIncomeOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_65aaa223-eca3-4b85-b25e-0685da3589e4" xlink:to="loc_us-gaap_InterestIncomeOperating_be7d457f-5a37-4dff-9967-6a04edecc69b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_37649f19-b5ce-430c-896e-43c5a91e2c60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_65aaa223-eca3-4b85-b25e-0685da3589e4" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_37649f19-b5ce-430c-896e-43c5a91e2c60" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/RevenuesNarrativeDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#RevenuesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/RevenuesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_04ae92d2-291e-44ba-8cf8-350e28434dc4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_03594e22-25ac-4925-968a-794b14c6649f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_04ae92d2-291e-44ba-8cf8-350e28434dc4" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_03594e22-25ac-4925-968a-794b14c6649f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_a9e79b6c-d562-41b0-a194-331c2a05f2ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_03594e22-25ac-4925-968a-794b14c6649f" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_a9e79b6c-d562-41b0-a194-331c2a05f2ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_18540b89-622e-4d71-ba7d-58d6fdcab633" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_04ae92d2-291e-44ba-8cf8-350e28434dc4" xlink:to="loc_us-gaap_ContractWithCustomerLiability_18540b89-622e-4d71-ba7d-58d6fdcab633" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_7567df5f-338e-492a-a917-6fe88c11de67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_04ae92d2-291e-44ba-8cf8-350e28434dc4" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_7567df5f-338e-492a-a917-6fe88c11de67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_a62fef03-b36a-4311-bad3-dca303d447fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerAssetNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_04ae92d2-291e-44ba-8cf8-350e28434dc4" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_a62fef03-b36a-4311-bad3-dca303d447fd" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/RevenuesNarrativeDetails_1" xlink:type="simple" xlink:href="prth-20250630.xsd#RevenuesNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://prth.com/role/RevenuesNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_04ae92d2-291e-44ba-8cf8-350e28434dc4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_03594e22-25ac-4925-968a-794b14c6649f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_04ae92d2-291e-44ba-8cf8-350e28434dc4" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_03594e22-25ac-4925-968a-794b14c6649f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_18540b89-622e-4d71-ba7d-58d6fdcab633" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_04ae92d2-291e-44ba-8cf8-350e28434dc4" xlink:to="loc_us-gaap_ContractWithCustomerLiability_18540b89-622e-4d71-ba7d-58d6fdcab633" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_7567df5f-338e-492a-a917-6fe88c11de67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_04ae92d2-291e-44ba-8cf8-350e28434dc4" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_7567df5f-338e-492a-a917-6fe88c11de67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_a62fef03-b36a-4311-bad3-dca303d447fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerAssetNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_04ae92d2-291e-44ba-8cf8-350e28434dc4" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_a62fef03-b36a-4311-bad3-dca303d447fd" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/SettlementAssetsandObligationsNarrativeDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#SettlementAssetsandObligationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/SettlementAssetsandObligationsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_387bcf11-3e90-41fe-ad55-e2c04e6526ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_7eea5dae-0ebe-4ccc-9836-b66975e9fd42" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_387bcf11-3e90-41fe-ad55-e2c04e6526ba" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_7eea5dae-0ebe-4ccc-9836-b66975e9fd42" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_cf401c9d-0992-4692-b6c2-9334379ad8dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_7eea5dae-0ebe-4ccc-9836-b66975e9fd42" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_cf401c9d-0992-4692-b6c2-9334379ad8dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_cf401c9d-0992-4692-b6c2-9334379ad8dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_cf401c9d-0992-4692-b6c2-9334379ad8dc" xlink:to="loc_us-gaap_ReceivableTypeDomain_cf401c9d-0992-4692-b6c2-9334379ad8dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_5d2145c5-2927-4430-b15e-5e04e66145b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_cf401c9d-0992-4692-b6c2-9334379ad8dc" xlink:to="loc_us-gaap_ReceivableTypeDomain_5d2145c5-2927-4430-b15e-5e04e66145b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CardSettlementsDueFromMerchantsMember_78a04950-9de2-4711-b057-c392a2074e00" xlink:href="prth-20250630.xsd#prth_CardSettlementsDueFromMerchantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_5d2145c5-2927-4430-b15e-5e04e66145b3" xlink:to="loc_prth_CardSettlementsDueFromMerchantsMember_78a04950-9de2-4711-b057-c392a2074e00" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_9966f0a4-8225-45a8-a6a9-ddc62452c155" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_7eea5dae-0ebe-4ccc-9836-b66975e9fd42" xlink:to="loc_srt_ProductOrServiceAxis_9966f0a4-8225-45a8-a6a9-ddc62452c155" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_9966f0a4-8225-45a8-a6a9-ddc62452c155_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_9966f0a4-8225-45a8-a6a9-ddc62452c155" xlink:to="loc_srt_ProductsAndServicesDomain_9966f0a4-8225-45a8-a6a9-ddc62452c155_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_843a8214-1505-448f-9c1b-004219f43eb1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_9966f0a4-8225-45a8-a6a9-ddc62452c155" xlink:to="loc_srt_ProductsAndServicesDomain_843a8214-1505-448f-9c1b-004219f43eb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_MoneyTransmissionsServicesMember_26a1a933-4275-467d-8c27-2364b4393e08" xlink:href="prth-20250630.xsd#prth_MoneyTransmissionsServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_843a8214-1505-448f-9c1b-004219f43eb1" xlink:to="loc_prth_MoneyTransmissionsServicesMember_26a1a933-4275-467d-8c27-2364b4393e08" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_AccountsReceivableAllowanceForCreditLossWriteoffRecovery_08a89227-0033-43ea-8758-204559f97108" xlink:href="prth-20250630.xsd#prth_AccountsReceivableAllowanceForCreditLossWriteoffRecovery"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_387bcf11-3e90-41fe-ad55-e2c04e6526ba" xlink:to="loc_prth_AccountsReceivableAllowanceForCreditLossWriteoffRecovery_08a89227-0033-43ea-8758-204559f97108" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfStatesInWhichEntityOperates_7354e8ce-8158-405c-95c1-dda5fb7d5ea0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfStatesInWhichEntityOperates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_387bcf11-3e90-41fe-ad55-e2c04e6526ba" xlink:to="loc_us-gaap_NumberOfStatesInWhichEntityOperates_7354e8ce-8158-405c-95c1-dda5fb7d5ea0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_NumberOfTerritoriesInWhichEntityOperates_079d35cc-a13d-4f47-9e1e-580773d4852a" xlink:href="prth-20250630.xsd#prth_NumberOfTerritoriesInWhichEntityOperates"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_387bcf11-3e90-41fe-ad55-e2c04e6526ba" xlink:to="loc_prth_NumberOfTerritoriesInWhichEntityOperates_079d35cc-a13d-4f47-9e1e-580773d4852a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/SettlementAssetsandObligationsScheduleofSettlementAssetsandObligationsDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#SettlementAssetsandObligationsScheduleofSettlementAssetsandObligationsDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/SettlementAssetsandObligationsScheduleofSettlementAssetsandObligationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_ef4a8c64-3604-48b9-94eb-90bb48242dfa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesAndLoansReceivableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_f97c96b2-9b31-4943-b95f-043fb554c46e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_ef4a8c64-3604-48b9-94eb-90bb48242dfa" xlink:to="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_f97c96b2-9b31-4943-b95f-043fb554c46e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_bfb6a7c0-c3bd-4554-b41e-251d6a6d22ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_f97c96b2-9b31-4943-b95f-043fb554c46e" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_bfb6a7c0-c3bd-4554-b41e-251d6a6d22ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_bfb6a7c0-c3bd-4554-b41e-251d6a6d22ca_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_bfb6a7c0-c3bd-4554-b41e-251d6a6d22ca" xlink:to="loc_us-gaap_ReceivableTypeDomain_bfb6a7c0-c3bd-4554-b41e-251d6a6d22ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_c619da48-2d34-4399-a9c5-ceb6f2e9af75" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_bfb6a7c0-c3bd-4554-b41e-251d6a6d22ca" xlink:to="loc_us-gaap_ReceivableTypeDomain_c619da48-2d34-4399-a9c5-ceb6f2e9af75" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CardSettlementsAndOtherSettlementAssetsMember_b79206bc-7d0f-4624-b379-ea4d586a7242" xlink:href="prth-20250630.xsd#prth_CardSettlementsAndOtherSettlementAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_c619da48-2d34-4399-a9c5-ceb6f2e9af75" xlink:to="loc_prth_CardSettlementsAndOtherSettlementAssetsMember_b79206bc-7d0f-4624-b379-ea4d586a7242" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CardSettlementsDueFromMerchantsMember_f3f01ecb-b10f-40e5-aa29-0bd06c56405e" xlink:href="prth-20250630.xsd#prth_CardSettlementsDueFromMerchantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_CardSettlementsAndOtherSettlementAssetsMember_b79206bc-7d0f-4624-b379-ea4d586a7242" xlink:to="loc_prth_CardSettlementsDueFromMerchantsMember_f3f01ecb-b10f-40e5-aa29-0bd06c56405e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CardSettlementsDueFromNetworksMember_77ea9ce0-4314-4911-896a-8ecf585537e3" xlink:href="prth-20250630.xsd#prth_CardSettlementsDueFromNetworksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_CardSettlementsAndOtherSettlementAssetsMember_b79206bc-7d0f-4624-b379-ea4d586a7242" xlink:to="loc_prth_CardSettlementsDueFromNetworksMember_77ea9ce0-4314-4911-896a-8ecf585537e3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_OtherSettlementAssetsMember_5725ead7-c2f2-4475-8fb3-72806aeca514" xlink:href="prth-20250630.xsd#prth_OtherSettlementAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_CardSettlementsAndOtherSettlementAssetsMember_b79206bc-7d0f-4624-b379-ea4d586a7242" xlink:to="loc_prth_OtherSettlementAssetsMember_5725ead7-c2f2-4475-8fb3-72806aeca514" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CardSettlementsDueFromMerchantFundsHeldAtMemberBanksMember_7efdd365-b64b-4d58-b300-001f8403afb7" xlink:href="prth-20250630.xsd#prth_CardSettlementsDueFromMerchantFundsHeldAtMemberBanksMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_c619da48-2d34-4399-a9c5-ceb6f2e9af75" xlink:to="loc_prth_CardSettlementsDueFromMerchantFundsHeldAtMemberBanksMember_7efdd365-b64b-4d58-b300-001f8403afb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_e11c09ad-99ae-4bde-aaa9-0d4ef5a9567b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_f97c96b2-9b31-4943-b95f-043fb554c46e" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_e11c09ad-99ae-4bde-aaa9-0d4ef5a9567b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e11c09ad-99ae-4bde-aaa9-0d4ef5a9567b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_e11c09ad-99ae-4bde-aaa9-0d4ef5a9567b" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_e11c09ad-99ae-4bde-aaa9-0d4ef5a9567b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_f617ee31-1655-4a27-83e4-8b9a308970f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_e11c09ad-99ae-4bde-aaa9-0d4ef5a9567b" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_f617ee31-1655-4a27-83e4-8b9a308970f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsMember_4dbe3fb6-02bc-41d1-968d-5b2de415174e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_f617ee31-1655-4a27-83e4-8b9a308970f3" xlink:to="loc_us-gaap_CashAndCashEquivalentsMember_4dbe3fb6-02bc-41d1-968d-5b2de415174e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_2eac10f6-58ea-4eb7-9bc1-dc732f6b07b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_f97c96b2-9b31-4943-b95f-043fb554c46e" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_2eac10f6-58ea-4eb7-9bc1-dc732f6b07b2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2eac10f6-58ea-4eb7-9bc1-dc732f6b07b2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_2eac10f6-58ea-4eb7-9bc1-dc732f6b07b2" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_2eac10f6-58ea-4eb7-9bc1-dc732f6b07b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_f35313b1-aa58-4913-b05a-ed712ae3f908" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_2eac10f6-58ea-4eb7-9bc1-dc732f6b07b2" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_f35313b1-aa58-4913-b05a-ed712ae3f908" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CustomerAndSubscriberAccountObligationsMember_2e97d0f3-2cdf-4106-8f59-251d1d9f942c" xlink:href="prth-20250630.xsd#prth_CustomerAndSubscriberAccountObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_f35313b1-aa58-4913-b05a-ed712ae3f908" xlink:to="loc_prth_CustomerAndSubscriberAccountObligationsMember_2e97d0f3-2cdf-4106-8f59-251d1d9f942c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CustomerAccountObligationsMember_24a8ec9e-75ee-402b-9c4b-1c7d113012c4" xlink:href="prth-20250630.xsd#prth_CustomerAccountObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_CustomerAndSubscriberAccountObligationsMember_2e97d0f3-2cdf-4106-8f59-251d1d9f942c" xlink:to="loc_prth_CustomerAccountObligationsMember_24a8ec9e-75ee-402b-9c4b-1c7d113012c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_SubscriberAccountObligationsMember_11e49484-cbe3-4620-b8d7-5661a46e07de" xlink:href="prth-20250630.xsd#prth_SubscriberAccountObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_CustomerAndSubscriberAccountObligationsMember_2e97d0f3-2cdf-4106-8f59-251d1d9f942c" xlink:to="loc_prth_SubscriberAccountObligationsMember_11e49484-cbe3-4620-b8d7-5661a46e07de" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_DueToCustomerPayeesMember_2825f17b-eddc-454c-8e15-fe9630b182e8" xlink:href="prth-20250630.xsd#prth_DueToCustomerPayeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_f35313b1-aa58-4913-b05a-ed712ae3f908" xlink:to="loc_prth_DueToCustomerPayeesMember_2825f17b-eddc-454c-8e15-fe9630b182e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_b742cce6-4f0b-434e-bb08-93798c501186" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAccountsNotesLoansAndFinancingReceivableTable_f97c96b2-9b31-4943-b95f-043fb554c46e" xlink:to="loc_dei_LegalEntityAxis_b742cce6-4f0b-434e-bb08-93798c501186" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_b742cce6-4f0b-434e-bb08-93798c501186_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_b742cce6-4f0b-434e-bb08-93798c501186" xlink:to="loc_dei_EntityDomain_b742cce6-4f0b-434e-bb08-93798c501186_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_0a91bdb4-f91a-4947-9a7d-756d9e429246" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_b742cce6-4f0b-434e-bb08-93798c501186" xlink:to="loc_dei_EntityDomain_0a91bdb4-f91a-4947-9a7d-756d9e429246" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_BankMember_44b168bb-19ea-4818-a683-328857a41a9c" xlink:href="prth-20250630.xsd#prth_BankMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_0a91bdb4-f91a-4947-9a7d-756d9e429246" xlink:to="loc_prth_BankMember_44b168bb-19ea-4818-a683-328857a41a9c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_SettlementAssetsAbstract_bf83b0c7-01e4-4d1e-9242-8f89fbf1cd51" xlink:href="prth-20250630.xsd#prth_SettlementAssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_ef4a8c64-3604-48b9-94eb-90bb48242dfa" xlink:to="loc_prth_SettlementAssetsAbstract_bf83b0c7-01e4-4d1e-9242-8f89fbf1cd51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SettlementAssetsCurrent_d7b44755-6075-4186-8208-d497c782cb83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SettlementAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_SettlementAssetsAbstract_bf83b0c7-01e4-4d1e-9242-8f89fbf1cd51" xlink:to="loc_us-gaap_SettlementAssetsCurrent_d7b44755-6075-4186-8208-d497c782cb83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_SettlementLiabilitiesAbstract_f7a76e3a-d3bf-4ab7-bd7b-17a461c021e7" xlink:href="prth-20250630.xsd#prth_SettlementLiabilitiesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_ef4a8c64-3604-48b9-94eb-90bb48242dfa" xlink:to="loc_prth_SettlementLiabilitiesAbstract_f7a76e3a-d3bf-4ab7-bd7b-17a461c021e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SettlementLiabilitiesCurrent_8ec8b78b-c649-473f-bfab-17fe2723a1b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SettlementLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_SettlementLiabilitiesAbstract_f7a76e3a-d3bf-4ab7-bd7b-17a461c021e7" xlink:to="loc_us-gaap_SettlementLiabilitiesCurrent_8ec8b78b-c649-473f-bfab-17fe2723a1b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_SettlementAssetsAllowanceForCreditLossCurrent_6c40b2ad-d094-4f17-9d40-328d24a36451" xlink:href="prth-20250630.xsd#prth_SettlementAssetsAllowanceForCreditLossCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_ef4a8c64-3604-48b9-94eb-90bb48242dfa" xlink:to="loc_prth_SettlementAssetsAllowanceForCreditLossCurrent_6c40b2ad-d094-4f17-9d40-328d24a36451" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_DepositsAgencyOwnedAccounts_2482337b-3e7a-437c-b26f-0c96716342fb" xlink:href="prth-20250630.xsd#prth_DepositsAgencyOwnedAccounts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccountsNotesAndLoansReceivableLineItems_ef4a8c64-3604-48b9-94eb-90bb48242dfa" xlink:to="loc_prth_DepositsAgencyOwnedAccounts_2482337b-3e7a-437c-b26f-0c96716342fb" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/NotesReceivableNarrativeDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#NotesReceivableNarrativeDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/NotesReceivableNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_6054efa9-c62c-4ee8-8ae3-3a33194ecf14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_b08d858f-62ac-4af5-8e3f-8d296939182d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_6054efa9-c62c-4ee8-8ae3-3a33194ecf14" xlink:to="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_b08d858f-62ac-4af5-8e3f-8d296939182d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_64380e8c-c686-4a12-a961-557625d1b1bd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFinancingReceivableAllowanceForCreditLossesTable_b08d858f-62ac-4af5-8e3f-8d296939182d" xlink:to="loc_srt_RangeAxis_64380e8c-c686-4a12-a961-557625d1b1bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_64380e8c-c686-4a12-a961-557625d1b1bd_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_64380e8c-c686-4a12-a961-557625d1b1bd" xlink:to="loc_srt_RangeMember_64380e8c-c686-4a12-a961-557625d1b1bd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_00d06e52-37e3-412a-bdd6-79b0957f3752" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_64380e8c-c686-4a12-a961-557625d1b1bd" xlink:to="loc_srt_RangeMember_00d06e52-37e3-412a-bdd6-79b0957f3752" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_18044ff9-273d-400a-b780-d90c48c07db9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_00d06e52-37e3-412a-bdd6-79b0957f3752" xlink:to="loc_srt_MinimumMember_18044ff9-273d-400a-b780-d90c48c07db9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_3692a999-8611-4eb1-8f4d-e64b69486adc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_00d06e52-37e3-412a-bdd6-79b0957f3752" xlink:to="loc_srt_MaximumMember_3692a999-8611-4eb1-8f4d-e64b69486adc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableNet_b713336a-05e8-4740-a4c4-44422c57a924" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotesReceivableNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_6054efa9-c62c-4ee8-8ae3-3a33194ecf14" xlink:to="loc_us-gaap_NotesReceivableNet_b713336a-05e8-4740-a4c4-44422c57a924" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_NotesReceivableAverageInterestRate_801c8eb8-7267-4a79-a80c-e32ebeb04fad" xlink:href="prth-20250630.xsd#prth_NotesReceivableAverageInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_6054efa9-c62c-4ee8-8ae3-3a33194ecf14" xlink:to="loc_prth_NotesReceivableAverageInterestRate_801c8eb8-7267-4a79-a80c-e32ebeb04fad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_NotesReceivableTerm_b04a9e5a-7fae-40a5-ae99-b8577fcf4569" xlink:href="prth-20250630.xsd#prth_NotesReceivableTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancingReceivableAllowanceForCreditLossesLineItems_6054efa9-c62c-4ee8-8ae3-3a33194ecf14" xlink:to="loc_prth_NotesReceivableTerm_b04a9e5a-7fae-40a5-ae99-b8577fcf4569" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/PropertyEquipmentandSoftwareDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#PropertyEquipmentandSoftwareDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/PropertyEquipmentandSoftwareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_5df598b2-3cf9-4a27-9bd5-d098158f211c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_3c164e3f-dab0-497b-a79b-5dd125a266d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_5df598b2-3cf9-4a27-9bd5-d098158f211c" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_3c164e3f-dab0-497b-a79b-5dd125a266d2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d6737907-4c68-4cd4-8e32-3e24048cd2af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_3c164e3f-dab0-497b-a79b-5dd125a266d2" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d6737907-4c68-4cd4-8e32-3e24048cd2af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_d6737907-4c68-4cd4-8e32-3e24048cd2af_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d6737907-4c68-4cd4-8e32-3e24048cd2af" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_d6737907-4c68-4cd4-8e32-3e24048cd2af_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_d260564d-d638-4ba2-a542-8e32ffbcc1cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_d6737907-4c68-4cd4-8e32-3e24048cd2af" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_d260564d-d638-4ba2-a542-8e32ffbcc1cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_DepreciablePropertyPlantAndEquipmentMember_e45db07d-3f4f-4213-8b3f-6b159aad8ba4" xlink:href="prth-20250630.xsd#prth_DepreciablePropertyPlantAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_d260564d-d638-4ba2-a542-8e32ffbcc1cf" xlink:to="loc_prth_DepreciablePropertyPlantAndEquipmentMember_e45db07d-3f4f-4213-8b3f-6b159aad8ba4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_bbb37553-b92a-4ff2-ac4a-0df089a6f12b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_DepreciablePropertyPlantAndEquipmentMember_e45db07d-3f4f-4213-8b3f-6b159aad8ba4" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_bbb37553-b92a-4ff2-ac4a-0df089a6f12b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquipmentMember_883d8115-1c79-48f4-b5a3-39d194e3daef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_DepreciablePropertyPlantAndEquipmentMember_e45db07d-3f4f-4213-8b3f-6b159aad8ba4" xlink:to="loc_us-gaap_EquipmentMember_883d8115-1c79-48f4-b5a3-39d194e3daef" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_c64732f3-8a2c-45aa-9df8-ab9907a7e70a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_DepreciablePropertyPlantAndEquipmentMember_e45db07d-3f4f-4213-8b3f-6b159aad8ba4" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_c64732f3-8a2c-45aa-9df8-ab9907a7e70a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_2edc484e-ea76-4a64-a666-7e98a768a3f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_prth_DepreciablePropertyPlantAndEquipmentMember_e45db07d-3f4f-4213-8b3f-6b159aad8ba4" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_2edc484e-ea76-4a64-a666-7e98a768a3f9" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CapitalWorkInProgressMember_6aff22d3-3c85-4512-a0dd-c4d6229b38ec" xlink:href="prth-20250630.xsd#prth_CapitalWorkInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_d260564d-d638-4ba2-a542-8e32ffbcc1cf" xlink:to="loc_prth_CapitalWorkInProgressMember_6aff22d3-3c85-4512-a0dd-c4d6229b38ec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_1e9108a2-5fb1-425d-8ce1-7217d93c1d01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_5df598b2-3cf9-4a27-9bd5-d098158f211c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_1e9108a2-5fb1-425d-8ce1-7217d93c1d01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_75b3f14a-3775-4dcc-bc03-0b45cf81caf8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_5df598b2-3cf9-4a27-9bd5-d098158f211c" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_75b3f14a-3775-4dcc-bc03-0b45cf81caf8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_d9f23328-018c-4b62-9969-380837830177" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_5df598b2-3cf9-4a27-9bd5-d098158f211c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_d9f23328-018c-4b62-9969-380837830177" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_0cd612fe-4bf4-455a-b004-a23fd07713c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_5df598b2-3cf9-4a27-9bd5-d098158f211c" xlink:to="loc_us-gaap_Depreciation_0cd612fe-4bf4-455a-b004-a23fd07713c5" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/GoodwillandOtherIntangibleAssetsGoodwillAllocationDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#GoodwillandOtherIntangibleAssetsGoodwillAllocationDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/GoodwillandOtherIntangibleAssetsGoodwillAllocationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillLineItems_9de1c702-6d8d-4fe5-ae79-1c9cd0e43c50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfGoodwillTable_37dc0b47-915e-414f-8dd0-67523bdb58af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfGoodwillTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_GoodwillLineItems_9de1c702-6d8d-4fe5-ae79-1c9cd0e43c50" xlink:to="loc_us-gaap_ScheduleOfGoodwillTable_37dc0b47-915e-414f-8dd0-67523bdb58af" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_18f84238-26ca-4565-906f-5ef241227b60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfGoodwillTable_37dc0b47-915e-414f-8dd0-67523bdb58af" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_18f84238-26ca-4565-906f-5ef241227b60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_18f84238-26ca-4565-906f-5ef241227b60_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_18f84238-26ca-4565-906f-5ef241227b60" xlink:to="loc_us-gaap_SegmentDomain_18f84238-26ca-4565-906f-5ef241227b60_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_cf0dc93b-b968-43b2-8dbf-1198c4112d64" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_18f84238-26ca-4565-906f-5ef241227b60" xlink:to="loc_us-gaap_SegmentDomain_cf0dc93b-b968-43b2-8dbf-1198c4112d64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_SMBPaymentsSegmentMember_b139df55-350a-47e7-b6f8-2056d3219869" xlink:href="prth-20250630.xsd#prth_SMBPaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_cf0dc93b-b968-43b2-8dbf-1198c4112d64" xlink:to="loc_prth_SMBPaymentsSegmentMember_b139df55-350a-47e7-b6f8-2056d3219869" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_EnterprisePaymentsSegmentMember_307e4960-3999-4498-a519-d1d62f666ae7" xlink:href="prth-20250630.xsd#prth_EnterprisePaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_cf0dc93b-b968-43b2-8dbf-1198c4112d64" xlink:to="loc_prth_EnterprisePaymentsSegmentMember_307e4960-3999-4498-a519-d1d62f666ae7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_B2BPaymentsSegmentMember_498daa96-6614-4802-b9ac-26ca7b7d0982" xlink:href="prth-20250630.xsd#prth_B2BPaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_cf0dc93b-b968-43b2-8dbf-1198c4112d64" xlink:to="loc_prth_B2BPaymentsSegmentMember_498daa96-6614-4802-b9ac-26ca7b7d0982" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_957d9fc8-db27-4250-a1e7-eebda00c0ef2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GoodwillLineItems_9de1c702-6d8d-4fe5-ae79-1c9cd0e43c50" xlink:to="loc_us-gaap_Goodwill_957d9fc8-db27-4250-a1e7-eebda00c0ef2" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/GoodwillandOtherIntangibleAssetsIntangibleAssetsDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#GoodwillandOtherIntangibleAssetsIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/GoodwillandOtherIntangibleAssetsIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_976b515e-0bb3-427b-ba57-79c93871f9e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2663f013-37c4-4799-9a4e-ad1b261fad86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_976b515e-0bb3-427b-ba57-79c93871f9e9" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2663f013-37c4-4799-9a4e-ad1b261fad86" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_f6b962b3-b17d-4e6f-aa49-320d1af16970" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_2663f013-37c4-4799-9a4e-ad1b261fad86" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_f6b962b3-b17d-4e6f-aa49-320d1af16970" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f6b962b3-b17d-4e6f-aa49-320d1af16970_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_f6b962b3-b17d-4e6f-aa49-320d1af16970" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_f6b962b3-b17d-4e6f-aa49-320d1af16970_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94f0d6fa-e2fb-41ce-b5c1-7df8a72dda92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_f6b962b3-b17d-4e6f-aa49-320d1af16970" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94f0d6fa-e2fb-41ce-b5c1-7df8a72dda92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_ISOAndReferralPartnerRelationshipsMember_8c8457fe-b87f-4440-9b1d-ded67ac77b39" xlink:href="prth-20250630.xsd#prth_ISOAndReferralPartnerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94f0d6fa-e2fb-41ce-b5c1-7df8a72dda92" xlink:to="loc_prth_ISOAndReferralPartnerRelationshipsMember_8c8457fe-b87f-4440-9b1d-ded67ac77b39" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_ResidualBuyoutsMember_2e339690-86e8-4321-9d54-8d736cd56812" xlink:href="prth-20250630.xsd#prth_ResidualBuyoutsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94f0d6fa-e2fb-41ce-b5c1-7df8a72dda92" xlink:to="loc_prth_ResidualBuyoutsMember_2e339690-86e8-4321-9d54-8d736cd56812" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_1aa17d73-56b0-42df-8c90-f7d8d616029c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94f0d6fa-e2fb-41ce-b5c1-7df8a72dda92" xlink:to="loc_us-gaap_CustomerRelationshipsMember_1aa17d73-56b0-42df-8c90-f7d8d616029c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceAgreementsMember_14b38750-7721-489f-b15f-fd032800d243" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ServiceAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94f0d6fa-e2fb-41ce-b5c1-7df8a72dda92" xlink:to="loc_us-gaap_ServiceAgreementsMember_14b38750-7721-489f-b15f-fd032800d243" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_86fe56e6-4fc1-482b-8df7-b9670eb7386a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94f0d6fa-e2fb-41ce-b5c1-7df8a72dda92" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_86fe56e6-4fc1-482b-8df7-b9670eb7386a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_f46bbdae-71ed-4466-bfa2-8576e6f2d180" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94f0d6fa-e2fb-41ce-b5c1-7df8a72dda92" xlink:to="loc_us-gaap_TradeNamesMember_f46bbdae-71ed-4466-bfa2-8576e6f2d180" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_5ba263ed-3b89-43fe-aaab-6c846179f4ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncompeteAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_94f0d6fa-e2fb-41ce-b5c1-7df8a72dda92" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_5ba263ed-3b89-43fe-aaab-6c846179f4ab" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_eebd485d-275d-48bc-877a-90fd7feff4ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_976b515e-0bb3-427b-ba57-79c93871f9e9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_eebd485d-275d-48bc-877a-90fd7feff4ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_66b2036e-a00b-4263-8b68-47a5aa51e3b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_976b515e-0bb3-427b-ba57-79c93871f9e9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_66b2036e-a00b-4263-8b68-47a5aa51e3b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_779999cb-78ce-4763-a99b-0e98ef212b83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_976b515e-0bb3-427b-ba57-79c93871f9e9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_779999cb-78ce-4763-a99b-0e98ef212b83" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_21f40ab8-2a05-4266-8332-621eb477e9a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_976b515e-0bb3-427b-ba57-79c93871f9e9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_21f40ab8-2a05-4266-8332-621eb477e9a4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_dcf429b2-1e9d-43d1-ac31-8109b80ac6bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_1b0da610-6297-4bfe-a8d1-979cdf308585" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_dcf429b2-1e9d-43d1-ac31-8109b80ac6bf" xlink:to="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_1b0da610-6297-4bfe-a8d1-979cdf308585" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_5d979128-733b-46be-8f90-8490df99a476" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_1b0da610-6297-4bfe-a8d1-979cdf308585" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_5d979128-733b-46be-8f90-8490df99a476" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_5d979128-733b-46be-8f90-8490df99a476_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_5d979128-733b-46be-8f90-8490df99a476" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_5d979128-733b-46be-8f90-8490df99a476_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_92f43bba-b710-46c7-a41f-586bd4a0b1e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_5d979128-733b-46be-8f90-8490df99a476" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_92f43bba-b710-46c7-a41f-586bd4a0b1e3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicenseMember_ca52b867-3d94-45fb-a0e6-4a4655f6eaf2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LicenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_92f43bba-b710-46c7-a41f-586bd4a0b1e3" xlink:to="loc_us-gaap_LicenseMember_ca52b867-3d94-45fb-a0e6-4a4655f6eaf2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_f3203763-9062-4532-a403-f387a90e4794" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_dcf429b2-1e9d-43d1-ac31-8109b80ac6bf" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_f3203763-9062-4532-a403-f387a90e4794" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/DebtObligationsScheduleofLongTermDebtDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#DebtObligationsScheduleofLongTermDebtDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/DebtObligationsScheduleofLongTermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_9d5cc107-a46c-437c-ab76-e431d68c614f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_1b344ff4-5abe-40a0-a6c8-0320d8057911" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9d5cc107-a46c-437c-ab76-e431d68c614f" xlink:to="loc_us-gaap_DebtInstrumentTable_1b344ff4-5abe-40a0-a6c8-0320d8057911" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_754bc5ca-93e5-4feb-8304-54400135c4c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_1b344ff4-5abe-40a0-a6c8-0320d8057911" xlink:to="loc_us-gaap_DebtInstrumentAxis_754bc5ca-93e5-4feb-8304-54400135c4c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_754bc5ca-93e5-4feb-8304-54400135c4c5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_754bc5ca-93e5-4feb-8304-54400135c4c5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_754bc5ca-93e5-4feb-8304-54400135c4c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_67e44d01-69da-49ba-9152-0cdabff2fd60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_754bc5ca-93e5-4feb-8304-54400135c4c5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_67e44d01-69da-49ba-9152-0cdabff2fd60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_A2024CreditAgreementMember_a9e8f321-017e-4364-bf2a-3cc6c0a5db9b" xlink:href="prth-20250630.xsd#prth_A2024CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_67e44d01-69da-49ba-9152-0cdabff2fd60" xlink:to="loc_prth_A2024CreditAgreementMember_a9e8f321-017e-4364-bf2a-3cc6c0a5db9b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_cc5e3a8d-96a2-47bc-b412-83bf96d1c4fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_1b344ff4-5abe-40a0-a6c8-0320d8057911" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_cc5e3a8d-96a2-47bc-b412-83bf96d1c4fc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_cc5e3a8d-96a2-47bc-b412-83bf96d1c4fc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_cc5e3a8d-96a2-47bc-b412-83bf96d1c4fc" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_cc5e3a8d-96a2-47bc-b412-83bf96d1c4fc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_57e1387a-1ef5-4747-9a0e-2cd4cb4913ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_cc5e3a8d-96a2-47bc-b412-83bf96d1c4fc" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_57e1387a-1ef5-4747-9a0e-2cd4cb4913ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_20a3142c-2791-4bcb-9a60-f3910bb6d5a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_57e1387a-1ef5-4747-9a0e-2cd4cb4913ee" xlink:to="loc_us-gaap_LineOfCreditMember_20a3142c-2791-4bcb-9a60-f3910bb6d5a3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_4dc5203e-81b7-45fc-9788-c628d49dcf61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_57e1387a-1ef5-4747-9a0e-2cd4cb4913ee" xlink:to="loc_us-gaap_SecuredDebtMember_4dc5203e-81b7-45fc-9788-c628d49dcf61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_aee3af26-f08d-4303-8027-c3cdaa9acaa8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_1b344ff4-5abe-40a0-a6c8-0320d8057911" xlink:to="loc_us-gaap_CreditFacilityAxis_aee3af26-f08d-4303-8027-c3cdaa9acaa8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_aee3af26-f08d-4303-8027-c3cdaa9acaa8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_aee3af26-f08d-4303-8027-c3cdaa9acaa8" xlink:to="loc_us-gaap_CreditFacilityDomain_aee3af26-f08d-4303-8027-c3cdaa9acaa8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_82ae25f6-d2a8-4c9d-8cb7-30057c80f765" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_aee3af26-f08d-4303-8027-c3cdaa9acaa8" xlink:to="loc_us-gaap_CreditFacilityDomain_82ae25f6-d2a8-4c9d-8cb7-30057c80f765" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_433afb28-b72b-4503-b21e-69098a0d210d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_82ae25f6-d2a8-4c9d-8cb7-30057c80f765" xlink:to="loc_us-gaap_SecuredDebtMember_433afb28-b72b-4503-b21e-69098a0d210d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_ead18e6c-0a20-4bfb-acb7-5c66dd281f76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_82ae25f6-d2a8-4c9d-8cb7-30057c80f765" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_ead18e6c-0a20-4bfb-acb7-5c66dd281f76" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_96e20cd5-97f5-4807-bd37-fbfe51df70d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9d5cc107-a46c-437c-ab76-e431d68c614f" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_96e20cd5-97f5-4807-bd37-fbfe51df70d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_2d83f9cc-24ec-43ef-af68-87833b80c9a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9d5cc107-a46c-437c-ab76-e431d68c614f" xlink:to="loc_us-gaap_LongTermDebtCurrent_2d83f9cc-24ec-43ef-af68-87833b80c9a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_032377ea-0718-474a-a9e6-dd022c963c0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9d5cc107-a46c-437c-ab76-e431d68c614f" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_032377ea-0718-474a-a9e6-dd022c963c0e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_58c20d29-81e5-49c0-b20e-ac05d47a7920" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9d5cc107-a46c-437c-ab76-e431d68c614f" xlink:to="loc_us-gaap_LongTermDebt_58c20d29-81e5-49c0-b20e-ac05d47a7920" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_420ca1a5-0e8e-47d5-b437-032d211ed355" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9d5cc107-a46c-437c-ab76-e431d68c614f" xlink:to="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_420ca1a5-0e8e-47d5-b437-032d211ed355" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_3747caa3-812c-45f2-b58e-0f8dbd71b790" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_9d5cc107-a46c-437c-ab76-e431d68c614f" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_3747caa3-812c-45f2-b58e-0f8dbd71b790" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/DebtObligationsNarrativeDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#DebtObligationsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/DebtObligationsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_254e7997-d6fb-4fe3-8d68-3173edd698da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_0449f483-d990-4a04-b249-c5e55f305506" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_254e7997-d6fb-4fe3-8d68-3173edd698da" xlink:to="loc_us-gaap_DebtInstrumentTable_0449f483-d990-4a04-b249-c5e55f305506" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_c05793ad-fa90-450b-a103-cda7a907ee31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0449f483-d990-4a04-b249-c5e55f305506" xlink:to="loc_us-gaap_DebtInstrumentAxis_c05793ad-fa90-450b-a103-cda7a907ee31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c05793ad-fa90-450b-a103-cda7a907ee31_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_c05793ad-fa90-450b-a103-cda7a907ee31" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c05793ad-fa90-450b-a103-cda7a907ee31_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_765516a6-eaf6-4fe9-962b-a4c060b11897" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_c05793ad-fa90-450b-a103-cda7a907ee31" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_765516a6-eaf6-4fe9-962b-a4c060b11897" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_A2024CreditAgreementMember_94ba03a2-b930-4f77-8242-eafa60f0f5e4" xlink:href="prth-20250630.xsd#prth_A2024CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_765516a6-eaf6-4fe9-962b-a4c060b11897" xlink:to="loc_prth_A2024CreditAgreementMember_94ba03a2-b930-4f77-8242-eafa60f0f5e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_b3a86349-6586-4e32-9be6-760bc6b95e02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0449f483-d990-4a04-b249-c5e55f305506" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_b3a86349-6586-4e32-9be6-760bc6b95e02" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_b3a86349-6586-4e32-9be6-760bc6b95e02_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b3a86349-6586-4e32-9be6-760bc6b95e02" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_b3a86349-6586-4e32-9be6-760bc6b95e02_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_0e464c56-3455-4a63-a7eb-98335bc8623a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_b3a86349-6586-4e32-9be6-760bc6b95e02" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_0e464c56-3455-4a63-a7eb-98335bc8623a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_5d27a8bb-f727-4860-a87e-f3d03f9ab042" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_0e464c56-3455-4a63-a7eb-98335bc8623a" xlink:to="loc_us-gaap_LineOfCreditMember_5d27a8bb-f727-4860-a87e-f3d03f9ab042" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_65661e1c-800b-4ebf-b2a9-a9eb32ddcd79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0449f483-d990-4a04-b249-c5e55f305506" xlink:to="loc_us-gaap_CreditFacilityAxis_65661e1c-800b-4ebf-b2a9-a9eb32ddcd79" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_65661e1c-800b-4ebf-b2a9-a9eb32ddcd79_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_65661e1c-800b-4ebf-b2a9-a9eb32ddcd79" xlink:to="loc_us-gaap_CreditFacilityDomain_65661e1c-800b-4ebf-b2a9-a9eb32ddcd79_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_0186fb29-4fb5-498a-987a-7ffb4f92d3d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_65661e1c-800b-4ebf-b2a9-a9eb32ddcd79" xlink:to="loc_us-gaap_CreditFacilityDomain_0186fb29-4fb5-498a-987a-7ffb4f92d3d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_b95ca9f6-4847-4661-b0a9-1e9fbd5e903d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_0186fb29-4fb5-498a-987a-7ffb4f92d3d2" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_b95ca9f6-4847-4661-b0a9-1e9fbd5e903d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_DebtInstrumentCovenantThresholdAmountOutstanding_4a7cb005-23c8-42b2-ac5f-00466b9a7c37" xlink:href="prth-20250630.xsd#prth_DebtInstrumentCovenantThresholdAmountOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_254e7997-d6fb-4fe3-8d68-3173edd698da" xlink:to="loc_prth_DebtInstrumentCovenantThresholdAmountOutstanding_4a7cb005-23c8-42b2-ac5f-00466b9a7c37" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_DebtInstrumentCovenantMaximumNetLeverageRatioPeriodOne_66bdd3d4-bc53-496c-8d75-c72966f547a4" xlink:href="prth-20250630.xsd#prth_DebtInstrumentCovenantMaximumNetLeverageRatioPeriodOne"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_254e7997-d6fb-4fe3-8d68-3173edd698da" xlink:to="loc_prth_DebtInstrumentCovenantMaximumNetLeverageRatioPeriodOne_66bdd3d4-bc53-496c-8d75-c72966f547a4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_DebtInstrumentCovenantMaximumNetLeverageRatioPeriodTwo_e0894fa7-9508-4189-b855-bfabc97f093b" xlink:href="prth-20250630.xsd#prth_DebtInstrumentCovenantMaximumNetLeverageRatioPeriodTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_254e7997-d6fb-4fe3-8d68-3173edd698da" xlink:to="loc_prth_DebtInstrumentCovenantMaximumNetLeverageRatioPeriodTwo_e0894fa7-9508-4189-b855-bfabc97f093b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/StockbasedCompensationScheduleofEquityBasedCompensationDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#StockbasedCompensationScheduleofEquityBasedCompensationDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/StockbasedCompensationScheduleofEquityBasedCompensationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b0221dda-d50e-4816-9634-54a1b5d79f72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4f22ae08-fc37-4175-8a50-2e4791f48d5b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b0221dda-d50e-4816-9634-54a1b5d79f72" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4f22ae08-fc37-4175-8a50-2e4791f48d5b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_c8235d84-25ce-4bd5-8bd9-ca34bb23e4dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_4f22ae08-fc37-4175-8a50-2e4791f48d5b" xlink:to="loc_us-gaap_AwardTypeAxis_c8235d84-25ce-4bd5-8bd9-ca34bb23e4dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c8235d84-25ce-4bd5-8bd9-ca34bb23e4dd_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_c8235d84-25ce-4bd5-8bd9-ca34bb23e4dd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_c8235d84-25ce-4bd5-8bd9-ca34bb23e4dd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_006f1fc5-4630-4eaf-b7e4-72d04a66384c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_c8235d84-25ce-4bd5-8bd9-ca34bb23e4dd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_006f1fc5-4630-4eaf-b7e4-72d04a66384c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_2272705c-e8dd-4fc8-aa4e-a8e2f6088b81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_006f1fc5-4630-4eaf-b7e4-72d04a66384c" xlink:to="loc_us-gaap_EmployeeStockOptionMember_2272705c-e8dd-4fc8-aa4e-a8e2f6088b81" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_EquityIncentiveUnitsMember_b77ee3e7-50aa-490f-ba42-0e3cf17e5fec" xlink:href="prth-20250630.xsd#prth_EquityIncentiveUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_006f1fc5-4630-4eaf-b7e4-72d04a66384c" xlink:to="loc_prth_EquityIncentiveUnitsMember_b77ee3e7-50aa-490f-ba42-0e3cf17e5fec" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_LiabilityClassifiedCompensationExpenseMember_54e67ce9-3750-4029-882c-1e5b68f4614f" xlink:href="prth-20250630.xsd#prth_LiabilityClassifiedCompensationExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_006f1fc5-4630-4eaf-b7e4-72d04a66384c" xlink:to="loc_prth_LiabilityClassifiedCompensationExpenseMember_54e67ce9-3750-4029-882c-1e5b68f4614f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_e1e40d0b-a0ea-4d14-877c-8f9d345887f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_006f1fc5-4630-4eaf-b7e4-72d04a66384c" xlink:to="loc_us-gaap_EmployeeStockMember_e1e40d0b-a0ea-4d14-877c-8f9d345887f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_0e551f19-cdbf-42f1-9818-c5fca0c87c76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_b0221dda-d50e-4816-9634-54a1b5d79f72" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_0e551f19-cdbf-42f1-9818-c5fca0c87c76" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/StockbasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#StockbasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/StockbasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_be01ef20-36b0-4eb9-add5-9fa1e9dab2f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b1579ba3-9807-43eb-9724-f7d9817c8193" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_be01ef20-36b0-4eb9-add5-9fa1e9dab2f0" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b1579ba3-9807-43eb-9724-f7d9817c8193" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_a89906ef-5b86-4fad-b7d4-020c48fb4f1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b1579ba3-9807-43eb-9724-f7d9817c8193" xlink:to="loc_us-gaap_PlanNameAxis_a89906ef-5b86-4fad-b7d4-020c48fb4f1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_a89906ef-5b86-4fad-b7d4-020c48fb4f1a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_a89906ef-5b86-4fad-b7d4-020c48fb4f1a" xlink:to="loc_us-gaap_PlanNameDomain_a89906ef-5b86-4fad-b7d4-020c48fb4f1a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_30718b75-d86b-49a0-baae-b4b5be5923d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_a89906ef-5b86-4fad-b7d4-020c48fb4f1a" xlink:to="loc_us-gaap_PlanNameDomain_30718b75-d86b-49a0-baae-b4b5be5923d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_A2018EquityIncentivePlanMember_7bae4c9d-13cb-4657-b553-6380f708e641" xlink:href="prth-20250630.xsd#prth_A2018EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_30718b75-d86b-49a0-baae-b4b5be5923d4" xlink:to="loc_prth_A2018EquityIncentivePlanMember_7bae4c9d-13cb-4657-b553-6380f708e641" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_12fe4f14-758d-464b-9306-25909ebb57ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b1579ba3-9807-43eb-9724-f7d9817c8193" xlink:to="loc_us-gaap_AwardTypeAxis_12fe4f14-758d-464b-9306-25909ebb57ad" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_12fe4f14-758d-464b-9306-25909ebb57ad_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_12fe4f14-758d-464b-9306-25909ebb57ad" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_12fe4f14-758d-464b-9306-25909ebb57ad_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_45070838-78b5-40da-b58a-935a527b1e88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_12fe4f14-758d-464b-9306-25909ebb57ad" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_45070838-78b5-40da-b58a-935a527b1e88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_c836ea50-9a04-4761-b05e-56fa42ff53a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_45070838-78b5-40da-b58a-935a527b1e88" xlink:to="loc_us-gaap_EmployeeStockMember_c836ea50-9a04-4761-b05e-56fa42ff53a5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_5aa17950-ea16-48a4-bf21-bcb3a6ee5c11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_be01ef20-36b0-4eb9-add5-9fa1e9dab2f0" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_5aa17950-ea16-48a4-bf21-bcb3a6ee5c11" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_508a81b8-831c-4a76-bbd6-8eaa19ad3e1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_be01ef20-36b0-4eb9-add5-9fa1e9dab2f0" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_508a81b8-831c-4a76-bbd6-8eaa19ad3e1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_7465beb5-0de1-4948-9e00-51731542f06a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_be01ef20-36b0-4eb9-add5-9fa1e9dab2f0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_7465beb5-0de1-4948-9e00-51731542f06a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_8d54f468-564e-42f9-9c5c-9ba59518eb92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_be01ef20-36b0-4eb9-add5-9fa1e9dab2f0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_8d54f468-564e-42f9-9c5c-9ba59518eb92" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServiceHoursPerWeek_1a3fa0b7-44f4-474a-9fa9-456e55d7a95d" xlink:href="prth-20250630.xsd#prth_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServiceHoursPerWeek"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_be01ef20-36b0-4eb9-add5-9fa1e9dab2f0" xlink:to="loc_prth_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServiceHoursPerWeek_1a3fa0b7-44f4-474a-9fa9-456e55d7a95d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_e1bafbdf-db73-489e-824a-e90bfc4a4cc3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_be01ef20-36b0-4eb9-add5-9fa1e9dab2f0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_e1bafbdf-db73-489e-824a-e90bfc4a4cc3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_2f3034c3-5d05-45fc-b060-b67c7870469e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_be01ef20-36b0-4eb9-add5-9fa1e9dab2f0" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_2f3034c3-5d05-45fc-b060-b67c7870469e" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/RelatedPartyTransactionsDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#RelatedPartyTransactionsDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/RelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_8a5d1912-9a72-45c1-851e-64f64e01b7eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_99398e61-0908-4833-8077-af9abeb28ba0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_8a5d1912-9a72-45c1-851e-64f64e01b7eb" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_99398e61-0908-4833-8077-af9abeb28ba0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_71101ecf-8063-474a-9aa7-d091b8b7177b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_99398e61-0908-4833-8077-af9abeb28ba0" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_71101ecf-8063-474a-9aa7-d091b8b7177b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_71101ecf-8063-474a-9aa7-d091b8b7177b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_71101ecf-8063-474a-9aa7-d091b8b7177b" xlink:to="loc_us-gaap_RelatedPartyDomain_71101ecf-8063-474a-9aa7-d091b8b7177b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_96692cea-0ff8-4a69-91cd-cb8363f0170a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_71101ecf-8063-474a-9aa7-d091b8b7177b" xlink:to="loc_us-gaap_RelatedPartyDomain_96692cea-0ff8-4a69-91cd-cb8363f0170a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ChiefExecutiveOfficerMember_21a8b156-a61f-40df-b915-67279fada21e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ChiefExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_96692cea-0ff8-4a69-91cd-cb8363f0170a" xlink:to="loc_srt_ChiefExecutiveOfficerMember_21a8b156-a61f-40df-b915-67279fada21e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SubsidiariesMember_d468fa8a-430d-40df-b6e5-230dea6683d5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SubsidiariesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_96692cea-0ff8-4a69-91cd-cb8363f0170a" xlink:to="loc_srt_SubsidiariesMember_d468fa8a-430d-40df-b6e5-230dea6683d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ChiefOperatingOfficerMember_1f666642-8a45-43f9-b843-6a2c6c613282" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ChiefOperatingOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_96692cea-0ff8-4a69-91cd-cb8363f0170a" xlink:to="loc_srt_ChiefOperatingOfficerMember_1f666642-8a45-43f9-b843-6a2c6c613282" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsidiarySaleOfStockAxis_ae2cf6a2-efb6-4815-a1af-78377d55450b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_99398e61-0908-4833-8077-af9abeb28ba0" xlink:to="loc_us-gaap_SubsidiarySaleOfStockAxis_ae2cf6a2-efb6-4815-a1af-78377d55450b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_ae2cf6a2-efb6-4815-a1af-78377d55450b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_ae2cf6a2-efb6-4815-a1af-78377d55450b" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_ae2cf6a2-efb6-4815-a1af-78377d55450b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNameOfTransactionDomain_4a99cb3e-3a7c-46be-a3aa-32e8271ca0e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsidiarySaleOfStockAxis_ae2cf6a2-efb6-4815-a1af-78377d55450b" xlink:to="loc_us-gaap_SaleOfStockNameOfTransactionDomain_4a99cb3e-3a7c-46be-a3aa-32e8271ca0e6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_ShareExchangeMember_f7fe802c-d1ea-4426-9595-aa95cb78a224" xlink:href="prth-20250630.xsd#prth_ShareExchangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SaleOfStockNameOfTransactionDomain_4a99cb3e-3a7c-46be-a3aa-32e8271ca0e6" xlink:to="loc_prth_ShareExchangeMember_f7fe802c-d1ea-4426-9595-aa95cb78a224" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RedeemableNoncontrollingInterestEquityPreferredRedemptionValue_af40dbb6-4960-4f20-95f6-e541c36dee3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RedeemableNoncontrollingInterestEquityPreferredRedemptionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_8a5d1912-9a72-45c1-851e-64f64e01b7eb" xlink:to="loc_us-gaap_RedeemableNoncontrollingInterestEquityPreferredRedemptionValue_af40dbb6-4960-4f20-95f6-e541c36dee3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_RedeemableNoncontrollingInterestEquityPreferredAnnualPreferredYieldPercent_9ac79cf7-48a8-452b-ac04-e50fbbfa9f1a" xlink:href="prth-20250630.xsd#prth_RedeemableNoncontrollingInterestEquityPreferredAnnualPreferredYieldPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_8a5d1912-9a72-45c1-851e-64f64e01b7eb" xlink:to="loc_prth_RedeemableNoncontrollingInterestEquityPreferredAnnualPreferredYieldPercent_9ac79cf7-48a8-452b-ac04-e50fbbfa9f1a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_51e989b4-671b-47de-bb66-8892ca7a719b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_8a5d1912-9a72-45c1-851e-64f64e01b7eb" xlink:to="loc_us-gaap_SaleOfStockConsiderationReceivedOnTransaction_51e989b4-671b-47de-bb66-8892ca7a719b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_c3a867dc-f0b3-42f6-8972-23f6220a82cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_8a5d1912-9a72-45c1-851e-64f64e01b7eb" xlink:to="loc_us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction_c3a867dc-f0b3-42f6-8972-23f6220a82cf" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#CommitmentsandContingenciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_a09471a0-49a2-4af0-8a74-a167fb18b53c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsTable_0aedf657-2adb-4ac4-819c-89194fcbcef0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a09471a0-49a2-4af0-8a74-a167fb18b53c" xlink:to="loc_us-gaap_OtherCommitmentsTable_0aedf657-2adb-4ac4-819c-89194fcbcef0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationByTypeAxis_7b1ad6e4-e294-4f6d-bef5-31184041cdd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_0aedf657-2adb-4ac4-819c-89194fcbcef0" xlink:to="loc_us-gaap_ContingentConsiderationByTypeAxis_7b1ad6e4-e294-4f6d-bef5-31184041cdd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_7b1ad6e4-e294-4f6d-bef5-31184041cdd8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_7b1ad6e4-e294-4f6d-bef5-31184041cdd8" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_7b1ad6e4-e294-4f6d-bef5-31184041cdd8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContingentConsiderationTypeDomain_f5d42abe-e32d-4e02-a79e-12975756270a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContingentConsiderationTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ContingentConsiderationByTypeAxis_7b1ad6e4-e294-4f6d-bef5-31184041cdd8" xlink:to="loc_us-gaap_ContingentConsiderationTypeDomain_f5d42abe-e32d-4e02-a79e-12975756270a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_ThirdPartyProcessingFeesMember_19c757b4-7e65-4df1-b2bd-fe75f3d08899" xlink:href="prth-20250630.xsd#prth_ThirdPartyProcessingFeesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ContingentConsiderationTypeDomain_f5d42abe-e32d-4e02-a79e-12975756270a" xlink:to="loc_prth_ThirdPartyProcessingFeesMember_19c757b4-7e65-4df1-b2bd-fe75f3d08899" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsAxis_6b8e6115-6abb-4f5d-8484-197f268f4ac2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_0aedf657-2adb-4ac4-819c-89194fcbcef0" xlink:to="loc_us-gaap_OtherCommitmentsAxis_6b8e6115-6abb-4f5d-8484-197f268f4ac2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsDomain_6b8e6115-6abb-4f5d-8484-197f268f4ac2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_OtherCommitmentsAxis_6b8e6115-6abb-4f5d-8484-197f268f4ac2" xlink:to="loc_us-gaap_OtherCommitmentsDomain_6b8e6115-6abb-4f5d-8484-197f268f4ac2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsDomain_e6e5c8cf-9227-43be-a5f3-66c8fcc5e099" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_OtherCommitmentsAxis_6b8e6115-6abb-4f5d-8484-197f268f4ac2" xlink:to="loc_us-gaap_OtherCommitmentsDomain_e6e5c8cf-9227-43be-a5f3-66c8fcc5e099" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CapitalCommitmentsMember_89906748-63af-4e21-a5a0-4813555aa4eb" xlink:href="prth-20250630.xsd#prth_CapitalCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsDomain_e6e5c8cf-9227-43be-a5f3-66c8fcc5e099" xlink:to="loc_prth_CapitalCommitmentsMember_89906748-63af-4e21-a5a0-4813555aa4eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_InvestmentCommitmentsMember_e836275c-5d32-486b-ad26-65b5ff8709cd" xlink:href="prth-20250630.xsd#prth_InvestmentCommitmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsDomain_e6e5c8cf-9227-43be-a5f3-66c8fcc5e099" xlink:to="loc_prth_InvestmentCommitmentsMember_e836275c-5d32-486b-ad26-65b5ff8709cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_012b1fb1-9751-45b4-8437-8d7e16f1ac9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_0aedf657-2adb-4ac4-819c-89194fcbcef0" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_012b1fb1-9751-45b4-8437-8d7e16f1ac9b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_012b1fb1-9751-45b4-8437-8d7e16f1ac9b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_012b1fb1-9751-45b4-8437-8d7e16f1ac9b" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_012b1fb1-9751-45b4-8437-8d7e16f1ac9b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_0c1b917a-6a1c-41e5-bcc2-3f64f00643ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_012b1fb1-9751-45b4-8437-8d7e16f1ac9b" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_0c1b917a-6a1c-41e5-bcc2-3f64f00643ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CustomerAccountObligationsMember_cdbc0f38-729b-44b4-85d3-71337f49c9e0" xlink:href="prth-20250630.xsd#prth_CustomerAccountObligationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_0c1b917a-6a1c-41e5-bcc2-3f64f00643ce" xlink:to="loc_prth_CustomerAccountObligationsMember_cdbc0f38-729b-44b4-85d3-71337f49c9e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear_cfda0612-531b-4e84-9fa6-caa6c932e5a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a09471a0-49a2-4af0-8a74-a167fb18b53c" xlink:to="loc_us-gaap_PurchaseObligationFutureMinimumPaymentsRemainderOfFiscalYear_cfda0612-531b-4e84-9fa6-caa6c932e5a7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligationDueInNextTwelveMonths_15919315-0875-45de-8779-737c23a3deb1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseObligationDueInNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a09471a0-49a2-4af0-8a74-a167fb18b53c" xlink:to="loc_us-gaap_PurchaseObligationDueInNextTwelveMonths_15919315-0875-45de-8779-737c23a3deb1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitment_677351a3-93eb-41c9-9069-bd35171d6f2d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a09471a0-49a2-4af0-8a74-a167fb18b53c" xlink:to="loc_us-gaap_OtherCommitment_677351a3-93eb-41c9-9069-bd35171d6f2d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_PurchaseCommitmentMaximumContractualTerm_af36051d-d55c-46f6-bff8-a34293f9d1b4" xlink:href="prth-20250630.xsd#prth_PurchaseCommitmentMaximumContractualTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a09471a0-49a2-4af0-8a74-a167fb18b53c" xlink:to="loc_prth_PurchaseCommitmentMaximumContractualTerm_af36051d-d55c-46f6-bff8-a34293f9d1b4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_LossContingenciesDamagesSoughtAmountPerViolation_c7617ed8-a622-4088-8871-e66ef9465708" xlink:href="prth-20250630.xsd#prth_LossContingenciesDamagesSoughtAmountPerViolation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a09471a0-49a2-4af0-8a74-a167fb18b53c" xlink:to="loc_prth_LossContingenciesDamagesSoughtAmountPerViolation_c7617ed8-a622-4088-8871-e66ef9465708" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_30d1d39c-b50c-4a9c-8103-63ac1e0fa2cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LitigationSettlementAmountAwardedToOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a09471a0-49a2-4af0-8a74-a167fb18b53c" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedToOtherParty_30d1d39c-b50c-4a9c-8103-63ac1e0fa2cd" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SettlementLiabilitiesCurrent_da150eb4-346f-409c-bb0f-1094c45a4b07" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SettlementLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_a09471a0-49a2-4af0-8a74-a167fb18b53c" xlink:to="loc_us-gaap_SettlementLiabilitiesCurrent_da150eb4-346f-409c-bb0f-1094c45a4b07" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/CommitmentsandContingenciesDeferredConsiderationLiabilitiesDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#CommitmentsandContingenciesDeferredConsiderationLiabilitiesDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/CommitmentsandContingenciesDeferredConsiderationLiabilitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_51a9e82c-14e4-4836-9eeb-e3037ebef318" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_5089ff24-550a-45cf-bda4-4c09d03cdb98" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_51a9e82c-14e4-4836-9eeb-e3037ebef318" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_5089ff24-550a-45cf-bda4-4c09d03cdb98" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_bad15089-0cea-4823-9d33-872c1cf7252d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_5089ff24-550a-45cf-bda4-4c09d03cdb98" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_bad15089-0cea-4823-9d33-872c1cf7252d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_bad15089-0cea-4823-9d33-872c1cf7252d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_bad15089-0cea-4823-9d33-872c1cf7252d" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_bad15089-0cea-4823-9d33-872c1cf7252d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_0414f469-9114-4fde-b4ce-f7f4bf937103" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_bad15089-0cea-4823-9d33-872c1cf7252d" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_0414f469-9114-4fde-b4ce-f7f4bf937103" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_DeferredConsiderationMember_f3441964-ee04-474b-a375-c3bf9535d51d" xlink:href="prth-20250630.xsd#prth_DeferredConsiderationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_0414f469-9114-4fde-b4ce-f7f4bf937103" xlink:to="loc_prth_DeferredConsiderationMember_f3441964-ee04-474b-a375-c3bf9535d51d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_ContingentConsiderationMember_61618f0e-4531-4958-a047-0303f05ac621" xlink:href="prth-20250630.xsd#prth_ContingentConsiderationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_0414f469-9114-4fde-b4ce-f7f4bf937103" xlink:to="loc_prth_ContingentConsiderationMember_61618f0e-4531-4958-a047-0303f05ac621" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_2d183b4d-81e3-41db-b71a-ba6456845a7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_51a9e82c-14e4-4836-9eeb-e3037ebef318" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_2d183b4d-81e3-41db-b71a-ba6456845a7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_d6eba214-92c8-4fa3-8156-5695ca08f72b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_2d183b4d-81e3-41db-b71a-ba6456845a7d" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_d6eba214-92c8-4fa3-8156-5695ca08f72b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases_c5f6fdad-9959-47d7-8503-c13a5bd3bc3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_2d183b4d-81e3-41db-b71a-ba6456845a7d" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityPurchases_c5f6fdad-9959-47d7-8503-c13a5bd3bc3b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_fe234eb6-70d8-4eec-874b-0bb43f2e6fc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_2d183b4d-81e3-41db-b71a-ba6456845a7d" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisChangeInUnrealizedGainLoss_fe234eb6-70d8-4eec-874b-0bb43f2e6fc5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_a4eba9e2-101e-4e59-bcb1-8349ca13839d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_2d183b4d-81e3-41db-b71a-ba6456845a7d" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements_a4eba9e2-101e-4e59-bcb1-8349ca13839d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_2eec2e26-13cf-4dd6-b827-2c123af3c059" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/FairValueDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#FairValueDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/FairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2edbcda8-41b2-4a7c-b689-af5123e01a78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_faacb8ed-ac10-4f43-b5cd-49c9fa2de50a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2edbcda8-41b2-4a7c-b689-af5123e01a78" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_faacb8ed-ac10-4f43-b5cd-49c9fa2de50a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_0187bdde-68e5-4cbb-8d12-59c624958656" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_faacb8ed-ac10-4f43-b5cd-49c9fa2de50a" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_0187bdde-68e5-4cbb-8d12-59c624958656" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_0187bdde-68e5-4cbb-8d12-59c624958656_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_0187bdde-68e5-4cbb-8d12-59c624958656" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_0187bdde-68e5-4cbb-8d12-59c624958656_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_38503b20-c150-47c2-9269-2ae048b5d8e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_0187bdde-68e5-4cbb-8d12-59c624958656" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_38503b20-c150-47c2-9269-2ae048b5d8e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_5b23fe39-c752-4224-9836-775c97a751cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_38503b20-c150-47c2-9269-2ae048b5d8e4" xlink:to="loc_us-gaap_LineOfCreditMember_5b23fe39-c752-4224-9836-775c97a751cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_88990ccf-6471-40d0-8c3e-51f59fdcc077" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_faacb8ed-ac10-4f43-b5cd-49c9fa2de50a" xlink:to="loc_us-gaap_DebtInstrumentAxis_88990ccf-6471-40d0-8c3e-51f59fdcc077" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_88990ccf-6471-40d0-8c3e-51f59fdcc077_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_88990ccf-6471-40d0-8c3e-51f59fdcc077" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_88990ccf-6471-40d0-8c3e-51f59fdcc077_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_6e8f9e52-62d2-41a5-9a16-228aabdeef84" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_88990ccf-6471-40d0-8c3e-51f59fdcc077" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_6e8f9e52-62d2-41a5-9a16-228aabdeef84" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_A2024CreditAgreementMember_abb64c44-488e-4053-8efc-72b049daa1ab" xlink:href="prth-20250630.xsd#prth_A2024CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_6e8f9e52-62d2-41a5-9a16-228aabdeef84" xlink:to="loc_prth_A2024CreditAgreementMember_abb64c44-488e-4053-8efc-72b049daa1ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_736c7b55-8654-4ba0-8f40-8f0e46fa95c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_faacb8ed-ac10-4f43-b5cd-49c9fa2de50a" xlink:to="loc_us-gaap_CreditFacilityAxis_736c7b55-8654-4ba0-8f40-8f0e46fa95c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_736c7b55-8654-4ba0-8f40-8f0e46fa95c9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_736c7b55-8654-4ba0-8f40-8f0e46fa95c9" xlink:to="loc_us-gaap_CreditFacilityDomain_736c7b55-8654-4ba0-8f40-8f0e46fa95c9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_73ae32e2-f201-4883-bbc7-19b99890fd4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_736c7b55-8654-4ba0-8f40-8f0e46fa95c9" xlink:to="loc_us-gaap_CreditFacilityDomain_73ae32e2-f201-4883-bbc7-19b99890fd4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_364480f8-ba17-4b99-9ee1-0a48c465da66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_73ae32e2-f201-4883-bbc7-19b99890fd4c" xlink:to="loc_us-gaap_SecuredDebtMember_364480f8-ba17-4b99-9ee1-0a48c465da66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableFairValueDisclosure_f8e8534c-f00d-4387-8f84-1e5e7ee6d27a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotesReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2edbcda8-41b2-4a7c-b689-af5123e01a78" xlink:to="loc_us-gaap_NotesReceivableFairValueDisclosure_f8e8534c-f00d-4387-8f84-1e5e7ee6d27a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_83e6f767-2f91-486a-ab83-f3e8f69745ed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_2edbcda8-41b2-4a7c-b689-af5123e01a78" xlink:to="loc_us-gaap_LongTermDebtFairValue_83e6f767-2f91-486a-ab83-f3e8f69745ed" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/SegmentInformationReportableSegmentsandReconciliationtoIncomeLossBeforeIncomeTaxesDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#SegmentInformationReportableSegmentsandReconciliationtoIncomeLossBeforeIncomeTaxesDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/SegmentInformationReportableSegmentsandReconciliationtoIncomeLossBeforeIncomeTaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_dcefddc6-a2d7-4320-a84b-857c1390fc04" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e5979d2d-d7bd-4bd4-976f-8199f438aae2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_dcefddc6-a2d7-4320-a84b-857c1390fc04" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e5979d2d-d7bd-4bd4-976f-8199f438aae2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_3c05c66e-6949-4097-90b5-43550586b280" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e5979d2d-d7bd-4bd4-976f-8199f438aae2" xlink:to="loc_srt_ConsolidationItemsAxis_3c05c66e-6949-4097-90b5-43550586b280" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_3c05c66e-6949-4097-90b5-43550586b280_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_3c05c66e-6949-4097-90b5-43550586b280" xlink:to="loc_srt_ConsolidationItemsDomain_3c05c66e-6949-4097-90b5-43550586b280_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_f907c759-5d9a-46a4-a848-5930ba911531" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_3c05c66e-6949-4097-90b5-43550586b280" xlink:to="loc_srt_ConsolidationItemsDomain_f907c759-5d9a-46a4-a848-5930ba911531" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_77679c43-18df-413c-b878-4bf7d0311245" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_f907c759-5d9a-46a4-a848-5930ba911531" xlink:to="loc_us-gaap_OperatingSegmentsMember_77679c43-18df-413c-b878-4bf7d0311245" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_47aff55e-1a22-4945-a6ed-04c75fa81001" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_f907c759-5d9a-46a4-a848-5930ba911531" xlink:to="loc_us-gaap_IntersegmentEliminationMember_47aff55e-1a22-4945-a6ed-04c75fa81001" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_c18281c0-e27d-4c39-a12d-b91fc3b56643" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_e5979d2d-d7bd-4bd4-976f-8199f438aae2" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_c18281c0-e27d-4c39-a12d-b91fc3b56643" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_c18281c0-e27d-4c39-a12d-b91fc3b56643_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_c18281c0-e27d-4c39-a12d-b91fc3b56643" xlink:to="loc_us-gaap_SegmentDomain_c18281c0-e27d-4c39-a12d-b91fc3b56643_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_11c476ff-85c5-41c8-939b-6c081a5235ef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_c18281c0-e27d-4c39-a12d-b91fc3b56643" xlink:to="loc_us-gaap_SegmentDomain_11c476ff-85c5-41c8-939b-6c081a5235ef" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_SMBPaymentsSegmentMember_39d90647-7f9e-4ebd-a161-5b8db287b9c7" xlink:href="prth-20250630.xsd#prth_SMBPaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_11c476ff-85c5-41c8-939b-6c081a5235ef" xlink:to="loc_prth_SMBPaymentsSegmentMember_39d90647-7f9e-4ebd-a161-5b8db287b9c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_B2BPaymentsSegmentMember_5d6d3532-d453-494f-8c3d-29acbc090fcc" xlink:href="prth-20250630.xsd#prth_B2BPaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_11c476ff-85c5-41c8-939b-6c081a5235ef" xlink:to="loc_prth_B2BPaymentsSegmentMember_5d6d3532-d453-494f-8c3d-29acbc090fcc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_EnterprisePaymentsSegmentMember_991b4438-a75e-41ba-b9e3-b137993bf35b" xlink:href="prth-20250630.xsd#prth_EnterprisePaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_11c476ff-85c5-41c8-939b-6c081a5235ef" xlink:to="loc_prth_EnterprisePaymentsSegmentMember_991b4438-a75e-41ba-b9e3-b137993bf35b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a17cbb43-67be-42d8-8a24-f01663194f0e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_dcefddc6-a2d7-4320-a84b-857c1390fc04" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a17cbb43-67be-42d8-8a24-f01663194f0e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_e22d3fca-afa1-4c90-8f87-1a51a938797f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_dcefddc6-a2d7-4320-a84b-857c1390fc04" xlink:to="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_e22d3fca-afa1-4c90-8f87-1a51a938797f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherExpenses_4739ec66-baf5-40a4-ad84-40dafba79102" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_dcefddc6-a2d7-4320-a84b-857c1390fc04" xlink:to="loc_us-gaap_OtherExpenses_4739ec66-baf5-40a4-ad84-40dafba79102" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_7110d9bd-adb0-4ec8-9930-c02cc2b8f15a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_dcefddc6-a2d7-4320-a84b-857c1390fc04" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_7110d9bd-adb0-4ec8-9930-c02cc2b8f15a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_AdjustedEBITDA_729b0fea-f08f-49dd-b232-59be18fc6032" xlink:href="prth-20250630.xsd#prth_AdjustedEBITDA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_dcefddc6-a2d7-4320-a84b-857c1390fc04" xlink:to="loc_prth_AdjustedEBITDA_729b0fea-f08f-49dd-b232-59be18fc6032" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/SegmentInformationReconciliationofAdjustedEBITDAtoIncomeLossBeforeIncomeTaxesDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#SegmentInformationReconciliationofAdjustedEBITDAtoIncomeLossBeforeIncomeTaxesDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/SegmentInformationReconciliationofAdjustedEBITDAtoIncomeLossBeforeIncomeTaxesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_d9ffaeb9-e5cd-4f0a-aa91-6a4490743b0f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_322ad3d4-c46c-44e7-978e-fe2cebca2ebb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_d9ffaeb9-e5cd-4f0a-aa91-6a4490743b0f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_322ad3d4-c46c-44e7-978e-fe2cebca2ebb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_eb3f92b3-98ac-4d39-8a35-c8f9a85fa498" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_322ad3d4-c46c-44e7-978e-fe2cebca2ebb" xlink:to="loc_srt_ConsolidationItemsAxis_eb3f92b3-98ac-4d39-8a35-c8f9a85fa498" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_eb3f92b3-98ac-4d39-8a35-c8f9a85fa498_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_eb3f92b3-98ac-4d39-8a35-c8f9a85fa498" xlink:to="loc_srt_ConsolidationItemsDomain_eb3f92b3-98ac-4d39-8a35-c8f9a85fa498_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_5b7bdb62-a3cf-4b22-9543-cc52e2b81beb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_eb3f92b3-98ac-4d39-8a35-c8f9a85fa498" xlink:to="loc_srt_ConsolidationItemsDomain_5b7bdb62-a3cf-4b22-9543-cc52e2b81beb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CorporateReconcilingItemsAndEliminationsMember_f142ba45-8482-4923-a14b-9ec286669a87" xlink:href="prth-20250630.xsd#prth_CorporateReconcilingItemsAndEliminationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_5b7bdb62-a3cf-4b22-9543-cc52e2b81beb" xlink:to="loc_prth_CorporateReconcilingItemsAndEliminationsMember_f142ba45-8482-4923-a14b-9ec286669a87" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_08efac8a-9618-4117-9327-eb8b5e8bf6d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_5b7bdb62-a3cf-4b22-9543-cc52e2b81beb" xlink:to="loc_us-gaap_IntersegmentEliminationMember_08efac8a-9618-4117-9327-eb8b5e8bf6d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_d9ffaeb9-e5cd-4f0a-aa91-6a4490743b0f" xlink:to="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_AdjustedEBITDA_db1742d2-5e55-4d61-8600-12f437e69732" xlink:href="prth-20250630.xsd#prth_AdjustedEBITDA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:to="loc_prth_AdjustedEBITDA_db1742d2-5e55-4d61-8600-12f437e69732" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_7c9b7db2-0500-4a85-b59b-e102998a7263" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:to="loc_us-gaap_CostsAndExpenses_7c9b7db2-0500-4a85-b59b-e102998a7263" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a6423075-43b4-4d27-8689-33ed79aa3e32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a6423075-43b4-4d27-8689-33ed79aa3e32" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_5207b691-547e-4a81-97ea-308ffbe8ccac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:to="loc_us-gaap_DepreciationAndAmortization_5207b691-547e-4a81-97ea-308ffbe8ccac" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_f1a6a16e-3dbb-4fd8-969b-0cd6948da100" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:to="loc_us-gaap_InterestExpenseNonoperating_f1a6a16e-3dbb-4fd8-969b-0cd6948da100" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_GainLossOnRestructuringAndModificationOfDebt_7caa290f-f921-4974-88a2-188ea5bb4cf5" xlink:href="prth-20250630.xsd#prth_GainLossOnRestructuringAndModificationOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:to="loc_prth_GainLossOnRestructuringAndModificationOfDebt_7caa290f-f921-4974-88a2-188ea5bb4cf5" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherSellingGeneralAndAdministrativeExpense_002d690f-1764-4889-88c2-bcd852a769e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherSellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:to="loc_us-gaap_OtherSellingGeneralAndAdministrativeExpense_002d690f-1764-4889-88c2-bcd852a769e1" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_ShareBasedPaymentArrangementNoncashExpenseAdjusted_682a07b1-fce2-4c90-b7be-23e46310b1bf" xlink:href="prth-20250630.xsd#prth_ShareBasedPaymentArrangementNoncashExpenseAdjusted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:to="loc_prth_ShareBasedPaymentArrangementNoncashExpenseAdjusted_682a07b1-fce2-4c90-b7be-23e46310b1bf" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossAttributableToParent_0469ee9a-0706-4111-af05-8eac140bb568" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReconciliationFromSegmentTotalsToConsolidatedAbstract_fbf8db0a-34c9-4e8d-aaba-aa80d5398c93" xlink:to="loc_us-gaap_IncomeLossAttributableToParent_0469ee9a-0706-4111-af05-8eac140bb568" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/SegmentInformationAdjustmentsforCorporateItemsDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#SegmentInformationAdjustmentsforCorporateItemsDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/SegmentInformationAdjustmentsforCorporateItemsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_e13e8f38-8575-47d1-953f-74b21ed0ab5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_ae7af0e2-ccd8-4705-91af-1a49bfd3dd81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e13e8f38-8575-47d1-953f-74b21ed0ab5d" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_ae7af0e2-ccd8-4705-91af-1a49bfd3dd81" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_9ae98958-5f96-4e1a-b597-3802ab5f5e19" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_ae7af0e2-ccd8-4705-91af-1a49bfd3dd81" xlink:to="loc_srt_ConsolidationItemsAxis_9ae98958-5f96-4e1a-b597-3802ab5f5e19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_9ae98958-5f96-4e1a-b597-3802ab5f5e19_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_9ae98958-5f96-4e1a-b597-3802ab5f5e19" xlink:to="loc_srt_ConsolidationItemsDomain_9ae98958-5f96-4e1a-b597-3802ab5f5e19_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_2a06519b-bde1-4a54-ad47-51c269f8e94e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_9ae98958-5f96-4e1a-b597-3802ab5f5e19" xlink:to="loc_srt_ConsolidationItemsDomain_2a06519b-bde1-4a54-ad47-51c269f8e94e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntersegmentEliminationMember_a33e2031-3ff0-43d6-97fd-aa241ab48299" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntersegmentEliminationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_2a06519b-bde1-4a54-ad47-51c269f8e94e" xlink:to="loc_us-gaap_IntersegmentEliminationMember_a33e2031-3ff0-43d6-97fd-aa241ab48299" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_29548319-e02f-4a1d-85ff-51fe6d040ee3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_2a06519b-bde1-4a54-ad47-51c269f8e94e" xlink:to="loc_us-gaap_CorporateNonSegmentMember_29548319-e02f-4a1d-85ff-51fe6d040ee3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CorporateReconcilingItemsAndEliminationsMember_bceae535-bae4-42c3-8a05-8e5acf6ee9b8" xlink:href="prth-20250630.xsd#prth_CorporateReconcilingItemsAndEliminationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_2a06519b-bde1-4a54-ad47-51c269f8e94e" xlink:to="loc_prth_CorporateReconcilingItemsAndEliminationsMember_bceae535-bae4-42c3-8a05-8e5acf6ee9b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_3781a1c5-e801-46ca-943e-abb54b8e0364" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e13e8f38-8575-47d1-953f-74b21ed0ab5d" xlink:to="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_3781a1c5-e801-46ca-943e-abb54b8e0364" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherExpenses_b7cc2f18-16f2-4fe1-9108-8ab98b3d470e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e13e8f38-8575-47d1-953f-74b21ed0ab5d" xlink:to="loc_us-gaap_OtherExpenses_b7cc2f18-16f2-4fe1-9108-8ab98b3d470e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingOtherItemAmount_c171537f-6e8f-43c1-a243-544b826270b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingOtherItemAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e13e8f38-8575-47d1-953f-74b21ed0ab5d" xlink:to="loc_us-gaap_SegmentReportingOtherItemAmount_c171537f-6e8f-43c1-a243-544b826270b9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_d426c5ed-1604-4139-9323-7dc02168b735" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_e13e8f38-8575-47d1-953f-74b21ed0ab5d" xlink:to="loc_us-gaap_CostsAndExpenses_d426c5ed-1604-4139-9323-7dc02168b735" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/SegmentInformationDepreciationandAmortizationDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#SegmentInformationDepreciationandAmortizationDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/SegmentInformationDepreciationandAmortizationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_cf90ae94-fbdd-43bb-84e3-6126445d8d14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_123b3cf2-9dbc-4c8d-a6e5-ec0fc77763fd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_cf90ae94-fbdd-43bb-84e3-6126445d8d14" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_123b3cf2-9dbc-4c8d-a6e5-ec0fc77763fd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_930c784d-2116-4bf3-8c20-725e91a5fefa" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_123b3cf2-9dbc-4c8d-a6e5-ec0fc77763fd" xlink:to="loc_srt_ConsolidationItemsAxis_930c784d-2116-4bf3-8c20-725e91a5fefa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_930c784d-2116-4bf3-8c20-725e91a5fefa_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_930c784d-2116-4bf3-8c20-725e91a5fefa" xlink:to="loc_srt_ConsolidationItemsDomain_930c784d-2116-4bf3-8c20-725e91a5fefa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_db7cf5b7-a7ff-4b91-9582-b9429945d857" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_930c784d-2116-4bf3-8c20-725e91a5fefa" xlink:to="loc_srt_ConsolidationItemsDomain_db7cf5b7-a7ff-4b91-9582-b9429945d857" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_054c958b-220a-4561-9575-eacc3f58cc10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_db7cf5b7-a7ff-4b91-9582-b9429945d857" xlink:to="loc_us-gaap_OperatingSegmentsMember_054c958b-220a-4561-9575-eacc3f58cc10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_d3b0419a-a5db-4407-af07-ab0078af174c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_123b3cf2-9dbc-4c8d-a6e5-ec0fc77763fd" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_d3b0419a-a5db-4407-af07-ab0078af174c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_d3b0419a-a5db-4407-af07-ab0078af174c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_d3b0419a-a5db-4407-af07-ab0078af174c" xlink:to="loc_us-gaap_SegmentDomain_d3b0419a-a5db-4407-af07-ab0078af174c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_fa573be1-e1bd-462f-be16-b214f24c538d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_d3b0419a-a5db-4407-af07-ab0078af174c" xlink:to="loc_us-gaap_SegmentDomain_fa573be1-e1bd-462f-be16-b214f24c538d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_SMBPaymentsSegmentMember_e55a4602-5638-4785-8407-ebbee1dd3822" xlink:href="prth-20250630.xsd#prth_SMBPaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_fa573be1-e1bd-462f-be16-b214f24c538d" xlink:to="loc_prth_SMBPaymentsSegmentMember_e55a4602-5638-4785-8407-ebbee1dd3822" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_B2BPaymentsSegmentMember_33f1f6dd-40d1-4759-8e14-895be09b2df0" xlink:href="prth-20250630.xsd#prth_B2BPaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_fa573be1-e1bd-462f-be16-b214f24c538d" xlink:to="loc_prth_B2BPaymentsSegmentMember_33f1f6dd-40d1-4759-8e14-895be09b2df0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_EnterprisePaymentsSegmentMember_802b9cdf-c760-475c-b816-207b93d16175" xlink:href="prth-20250630.xsd#prth_EnterprisePaymentsSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_fa573be1-e1bd-462f-be16-b214f24c538d" xlink:to="loc_prth_EnterprisePaymentsSegmentMember_802b9cdf-c760-475c-b816-207b93d16175" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_fe059547-09eb-4bbc-8d3e-f6a5bb93671a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_cf90ae94-fbdd-43bb-84e3-6126445d8d14" xlink:to="loc_us-gaap_DepreciationAndAmortization_fe059547-09eb-4bbc-8d3e-f6a5bb93671a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/EarningsLossperCommonShareScheduleofAntidilutiveSecuritiesDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#EarningsLossperCommonShareScheduleofAntidilutiveSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/EarningsLossperCommonShareScheduleofAntidilutiveSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_f4015f57-f735-4543-a37e-b14d87909061" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_eaf3b4d4-7b05-4148-b2dc-9d63e5d56229" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_f4015f57-f735-4543-a37e-b14d87909061" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_eaf3b4d4-7b05-4148-b2dc-9d63e5d56229" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8b414abd-cdd7-4ee4-918e-1078cfb071f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_eaf3b4d4-7b05-4148-b2dc-9d63e5d56229" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8b414abd-cdd7-4ee4-918e-1078cfb071f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_8b414abd-cdd7-4ee4-918e-1078cfb071f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8b414abd-cdd7-4ee4-918e-1078cfb071f2" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_8b414abd-cdd7-4ee4-918e-1078cfb071f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_aa2cd950-6e91-4f4e-a4d4-dc8dba80b883" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_8b414abd-cdd7-4ee4-918e-1078cfb071f2" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_aa2cd950-6e91-4f4e-a4d4-dc8dba80b883" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_ad11ecc3-75d7-4b0e-a7fe-623be06201a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_aa2cd950-6e91-4f4e-a4d4-dc8dba80b883" xlink:to="loc_us-gaap_RestrictedStockMember_ad11ecc3-75d7-4b0e-a7fe-623be06201a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_LiabilityClassifiedRestrictedStockUnitsMember_594b9cb2-8237-47c7-8436-c4c7774fab12" xlink:href="prth-20250630.xsd#prth_LiabilityClassifiedRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_aa2cd950-6e91-4f4e-a4d4-dc8dba80b883" xlink:to="loc_prth_LiabilityClassifiedRestrictedStockUnitsMember_594b9cb2-8237-47c7-8436-c4c7774fab12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_d8fd8fd4-aa23-46a3-9d7d-9e17bcbcb96b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_aa2cd950-6e91-4f4e-a4d4-dc8dba80b883" xlink:to="loc_us-gaap_EmployeeStockOptionMember_d8fd8fd4-aa23-46a3-9d7d-9e17bcbcb96b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_d736c0c7-d9c2-4316-b4e8-94b69db0e52c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_f4015f57-f735-4543-a37e-b14d87909061" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_d736c0c7-d9c2-4316-b4e8-94b69db0e52c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_daa7faca-7b08-4529-af59-5479fec5b742" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_f4015f57-f735-4543-a37e-b14d87909061" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_daa7faca-7b08-4529-af59-5479fec5b742" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://prth.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="prth-20250630.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://prth.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_f19876e7-5528-45e4-9aac-5ab65e197694" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_a15ee129-094f-4aa8-84d8-6a2002f1375b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_f19876e7-5528-45e4-9aac-5ab65e197694" xlink:to="loc_us-gaap_SubsequentEventTable_a15ee129-094f-4aa8-84d8-6a2002f1375b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_8931065c-9923-4014-ac71-af22ad5572eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_a15ee129-094f-4aa8-84d8-6a2002f1375b" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_8931065c-9923-4014-ac71-af22ad5572eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_8931065c-9923-4014-ac71-af22ad5572eb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_8931065c-9923-4014-ac71-af22ad5572eb" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_8931065c-9923-4014-ac71-af22ad5572eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_ef8c6d16-eff4-4106-b8a6-906ce332f20b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_8931065c-9923-4014-ac71-af22ad5572eb" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_ef8c6d16-eff4-4106-b8a6-906ce332f20b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_ef74c167-75f0-46eb-9cbd-191b4bb7c2ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_ef8c6d16-eff4-4106-b8a6-906ce332f20b" xlink:to="loc_us-gaap_SubsequentEventMember_ef74c167-75f0-46eb-9cbd-191b4bb7c2ea" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_dbc521f7-52c1-4944-a74e-787964984193" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_a15ee129-094f-4aa8-84d8-6a2002f1375b" xlink:to="loc_us-gaap_CreditFacilityAxis_dbc521f7-52c1-4944-a74e-787964984193" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_dbc521f7-52c1-4944-a74e-787964984193_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_dbc521f7-52c1-4944-a74e-787964984193" xlink:to="loc_us-gaap_CreditFacilityDomain_dbc521f7-52c1-4944-a74e-787964984193_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_9f191473-28bb-41f0-8d9c-ace218e16e52" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_dbc521f7-52c1-4944-a74e-787964984193" xlink:to="loc_us-gaap_CreditFacilityDomain_9f191473-28bb-41f0-8d9c-ace218e16e52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_e2a1f853-82e0-4961-a704-c865a041710c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_9f191473-28bb-41f0-8d9c-ace218e16e52" xlink:to="loc_us-gaap_SecuredDebtMember_e2a1f853-82e0-4961-a704-c865a041710c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_2cd6a4c6-14c7-4798-8671-0a89bebb6b18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_9f191473-28bb-41f0-8d9c-ace218e16e52" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_2cd6a4c6-14c7-4798-8671-0a89bebb6b18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_ee7a8bc1-475b-45a1-a19b-c4ddc0ebe266" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_a15ee129-094f-4aa8-84d8-6a2002f1375b" xlink:to="loc_us-gaap_DebtInstrumentAxis_ee7a8bc1-475b-45a1-a19b-c4ddc0ebe266" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_ee7a8bc1-475b-45a1-a19b-c4ddc0ebe266_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_ee7a8bc1-475b-45a1-a19b-c4ddc0ebe266" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_ee7a8bc1-475b-45a1-a19b-c4ddc0ebe266_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_f4194f3d-8f3b-47dd-b79b-d369a653e457" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_ee7a8bc1-475b-45a1-a19b-c4ddc0ebe266" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_f4194f3d-8f3b-47dd-b79b-d369a653e457" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_CreditAgreementMember_a6620cf2-f89a-459a-94ba-7632a6963976" xlink:href="prth-20250630.xsd#prth_CreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_f4194f3d-8f3b-47dd-b79b-d369a653e457" xlink:to="loc_prth_CreditAgreementMember_a6620cf2-f89a-459a-94ba-7632a6963976" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_dcae5396-a220-4d3b-9cf0-da26bb8f4cc4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_a15ee129-094f-4aa8-84d8-6a2002f1375b" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_dcae5396-a220-4d3b-9cf0-da26bb8f4cc4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_dcae5396-a220-4d3b-9cf0-da26bb8f4cc4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_dcae5396-a220-4d3b-9cf0-da26bb8f4cc4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_dcae5396-a220-4d3b-9cf0-da26bb8f4cc4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_bfc1fb53-bf7a-4651-857c-30539f9911d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_dcae5396-a220-4d3b-9cf0-da26bb8f4cc4" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_bfc1fb53-bf7a-4651-857c-30539f9911d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_7a81235a-dca8-44ef-966b-c83f3066620a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_bfc1fb53-bf7a-4651-857c-30539f9911d3" xlink:to="loc_us-gaap_LineOfCreditMember_7a81235a-dca8-44ef-966b-c83f3066620a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_8943d005-2924-4ef1-a61e-46773b447efb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_a15ee129-094f-4aa8-84d8-6a2002f1375b" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_8943d005-2924-4ef1-a61e-46773b447efb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8943d005-2924-4ef1-a61e-46773b447efb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_8943d005-2924-4ef1-a61e-46773b447efb" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_8943d005-2924-4ef1-a61e-46773b447efb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3a712cc1-0f73-4ddb-b1a9-7e1dd0c12973" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_8943d005-2924-4ef1-a61e-46773b447efb" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3a712cc1-0f73-4ddb-b1a9-7e1dd0c12973" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_PlastiqMember_6a564555-3ecd-46ce-9ad3-29f7a599a69c" xlink:href="prth-20250630.xsd#prth_PlastiqMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3a712cc1-0f73-4ddb-b1a9-7e1dd0c12973" xlink:to="loc_prth_PlastiqMember_6a564555-3ecd-46ce-9ad3-29f7a599a69c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_prth_PoweredByPriorityLLCMember_329c85c7-7464-40d5-ad28-5cd52b703d90" xlink:href="prth-20250630.xsd#prth_PoweredByPriorityLLCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3a712cc1-0f73-4ddb-b1a9-7e1dd0c12973" xlink:to="loc_prth_PoweredByPriorityLLCMember_329c85c7-7464-40d5-ad28-5cd52b703d90" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_905bf3a0-277b-4194-9d56-b6e78d27ec28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_f19876e7-5528-45e4-9aac-5ab65e197694" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_905bf3a0-277b-4194-9d56-b6e78d27ec28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_2a843d3c-1f4b-4f9e-a86b-78173bc9676f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_f19876e7-5528-45e4-9aac-5ab65e197694" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_2a843d3c-1f4b-4f9e-a86b-78173bc9676f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_56f6fb8b-e461-421b-85af-98b1551424be" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_f19876e7-5528-45e4-9aac-5ab65e197694" xlink:to="loc_us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_56f6fb8b-e461-421b-85af-98b1551424be" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_c1442724-9340-4238-801b-63816df95d93" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_f19876e7-5528-45e4-9aac-5ab65e197694" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_c1442724-9340-4238-801b-63816df95d93" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
