Update beginChangeSubscriptionAmount() function

CRM/Core/Payment/MJWTrait.php

@@ -503,25 +503,19 @@ trait CRM_Core_Payment_MJWTrait {
      * ];
      */
     $propertyBag = PropertyBag::cast($params);
-    $propertyBag->setContributionRecurID($params['id']);
+    $propertyBag->setContributionRecurID($params['contributionRecurID'] ?? $params['id']);
     $propertyBag->setIsRecur(TRUE);
-    // @fixme We can't use $propertyBag->setRecurInstallments until https://github.com/civicrm/civicrm-core/pull/21517 is merged
-    //   Use $propertyBag->has('recurInstallments') ? $propertyBag->getRecurInstallments() : 0; in code as workaround
-    // if (empty($params['installments'])) {
-    //   $propertyBag->setRecurInstallments(0);
-    // }
+
     $existingRecur = ContributionRecur::get(FALSE)
       ->addWhere('is_test', 'IN', [TRUE, FALSE])
       ->addWhere('id', '=', $propertyBag->getContributionRecurID())
       ->execute()
       ->first();
 
-    // @fixme: https://github.com/civicrm/civicrm-core/pull/21517
-    if (!$propertyBag->has('recurInstallments') && !empty($existingRecur['installments'])) {
-      $propertyBag->setRecurInstallments($existingRecur['installments']);
-    }
+    $propertyBag->setRecurInstallments($existingRecur['installments'] ?? 0);
     $propertyBag->setRecurFrequencyInterval($existingRecur['frequency_interval']);
     $propertyBag->setRecurFrequencyUnit($existingRecur['frequency_unit']);
+    $propertyBag->setCurrency($params['currency'] ?? $existingRecur['currency']);
 
     $propertyBag->setCustomProperty('error_url', $this->getErrorUrl($propertyBag));