diff --git a/app/Services/OrderService.php b/app/Services/OrderService.php
index a08270a..accf11b 100644
--- a/app/Services/OrderService.php
+++ b/app/Services/OrderService.php
@@ -179,7 +179,7 @@ class OrderService extends BaseService
 
                 $options = array();
                 $options['transaction_id'] = $order['escrow_trade_no'];
-                $options['out_refund_no'] = $refund_no;
+                $options['out_refund_no'] = (string)$refund_no;
                 $options['reason'] = $refund_reason;
                 $options['amount'] = [
                     'refund' => (int)round($order['payment_amount_total'] * 100),