diff --git a/wchat/wx/V3/TransferDetail.php b/wchat/wx/V3/TransferDetail.php
index 5c7a6d3..be3ec48 100644
--- a/wchat/wx/V3/TransferDetail.php
+++ b/wchat/wx/V3/TransferDetail.php
@@ -8,11 +8,11 @@ class TransferDetail
 {
 
     public function __construct(
-        public string    $out_detail_no,
-        public int|float $transfer_amount,
-        public string    $transfer_remark,
-        public string    $openid,
-        public string    $user_name
+        readonly public string    $out_detail_no,
+        readonly public int|float $transfer_amount,
+        readonly public string    $transfer_remark,
+        readonly public string    $openid,
+        readonly public string    $user_name = ''
     )
     {
     }