Remove tax calculation from overpayment credit note

The overpayment amount is already the gross cash difference
(total_payments - contribution_total), where contribution_total
is tax-inclusive. Applying tax would inflate the credit note
beyond the actual overpayment, throwing accounting off balance.

Author: erawat

Civi/Api4/Action/CreditNote/AllocateOverpaymentAction.php

@@ -9,7 +9,6 @@
 use Civi\Api4\Contribution;
 use Civi\Api4\Company;
 use Civi\Api4\OptionValue;
-use Civi\Api4\EntityFinancialAccount;
 use Civi\Financeextras\Utils\OverpaymentUtils;
 use Civi\Financeextras\Event\ContributionPaymentUpdatedEvent;
 
@@ -168,8 +167,10 @@ private function createOverpaymentCreditNote(
       ->execute()
       ->first()['value'] ?? NULL;
 
-    // Get tax rate for the financial type if configured.
-    $taxRate = $this->getTaxRateForFinancialType($financialTypeId);
+    // Note: We do NOT apply tax to the overpayment amount.
+    // The overpayment is the excess cash paid (total_payments - contribution_total),
+    // where contribution_total is already tax-inclusive. Adding tax would create
+    // a credit note larger than the actual overpayment, throwing accounting off balance.
 
     return CreditNote::save(FALSE)
       ->addRecord([
@@ -186,35 +187,14 @@ private function createOverpaymentCreditNote(
             'financial_type_id' => $financialTypeId,
             'quantity' => 1,
             'unit_price' => $amount,
-            'tax_rate' => $taxRate,
+            'tax_rate' => 0,
           ],
         ],
       ])
       ->execute()
       ->first();
   }
 
-  /**
-   * Get the tax rate for a financial type.
-   *
-   * @param int $financialTypeId
-   *   The financial type ID.
-   *
-   * @return float
-   *   The tax rate (0 if no sales tax account is configured).
-   */
-  private function getTaxRateForFinancialType(int $financialTypeId): float {
-    $entityFinancialAccount = EntityFinancialAccount::get(FALSE)
-      ->addSelect('financial_account_id.tax_rate')
-      ->addWhere('account_relationship:name', '=', 'Sales Tax Account is')
-      ->addWhere('entity_table', '=', 'civicrm_financial_type')
-      ->addWhere('entity_id', '=', $financialTypeId)
-      ->execute()
-      ->first();
-
-    return (float) ($entityFinancialAccount['financial_account_id.tax_rate'] ?? 0);
-  }
-
   /**
    * Record overpayment adjustment on the contribution to balance it.
    *