normalize data po number to pr number and fix logic to fill field PO number

internal/modules/purchases/services/purchase.service.go

@@ -779,8 +779,7 @@ func (s *purchaseService) ApproveManagerPurchase(c *fiber.Ctx, id uint, req *val
 	transactionErr := s.PurchaseRepo.DB().WithContext(c.Context()).Transaction(func(tx *gorm.DB) error {
 		updateData := map[string]any{}
 		if !hasExistingPO {
-			repoTx := rPurchase.NewPurchaseRepository(tx)
-			code, err := repoTx.NextPoNumber(c.Context(), tx)
+			code, err := derivePoFromPr(purchase.PrNumber)
 			if err != nil {
 				return err
 			}
@@ -2513,6 +2512,18 @@ func parseApprovalActionInput(raw string) (entity.ApprovalAction, error) {
 	}
 }
 
+// derivePoFromPr menghasilkan po_number dari pr_number dengan swap prefix.
+// Contoh: "PR-LTI-0050" -> "PO-LTI-0050". Mengembalikan error kalau pr_number
+// tidak diawali prefix standar — caller harus memastikan PR sudah valid.
+func derivePoFromPr(prNumber string) (string, error) {
+	trimmed := strings.TrimSpace(prNumber)
+	if !strings.HasPrefix(trimmed, utils.PurchasePRNumberPrefix) {
+		return "", fmt.Errorf("invalid pr_number %q: missing prefix %q", trimmed, utils.PurchasePRNumberPrefix)
+	}
+	suffix := strings.TrimPrefix(trimmed, utils.PurchasePRNumberPrefix)
+	return utils.PurchasePONumberPrefix + suffix, nil
+}
+
 func (s *purchaseService) rejectAndReload(
 	c *fiber.Ctx,
 	step approvalutils.ApprovalStep,