diff --git a/WePayV3/Contracts/BasicWePay.php b/WePayV3/Contracts/BasicWePay.php
index 7ad6d7b..8f628f3 100644
--- a/WePayV3/Contracts/BasicWePay.php
+++ b/WePayV3/Contracts/BasicWePay.php
@@ -333,7 +333,15 @@ abstract class BasicWePay
     protected function signBuild($data)
     {
         $pkeyid = openssl_pkey_get_private($this->config['cert_private']);
-        openssl_sign($data, $signature, $pkeyid, 'sha256WithRSAEncryption');
+        if ($pkeyid === false) {
+            throw new InvalidArgumentException("Invalid private key -- [cert_private]");
+        }
+        $signature = '';
+        if (!openssl_sign($data, $signature, $pkeyid, 'sha256WithRSAEncryption')) {
+            openssl_free_key($pkeyid);
+            throw new InvalidArgumentException("Failed to sign data with private key");
+        }
+        openssl_free_key($pkeyid);
         return base64_encode($signature);
     }
 
diff --git a/WePayV3/Order.php b/WePayV3/Order.php
index c4866dc..2b18d25 100644
--- a/WePayV3/Order.php
+++ b/WePayV3/Order.php
@@ -52,6 +52,13 @@ class Order extends BasicWePay
         if (empty($types[$type])) {
             throw new InvalidArgumentException("Payment {$type} not defined.");
         } else {
+            // 自动填充 mchid 和 appid（如果未提供）
+            if (empty($data['mchid']) && !empty($this->config['mch_id'])) {
+                $data['mchid'] = $this->config['mch_id'];
+            }
+            if (empty($data['appid']) && !empty($this->config['appid'])) {
+                $data['appid'] = $this->config['appid'];
+            }
             // 创建预支付码
             $result = $this->doRequest('POST', $types[$type], json_encode($data, JSON_UNESCAPED_UNICODE), true);
             if (empty($result['h5_url']) && empty($result['code_url']) && empty($result['prepay_id'])) {