edit

lib/Wechat.php

@@ -112,7 +112,15 @@ class Wechat extends Core
 			$order['partnerid'] = $this->config->GetMerchantId();
 			$order['package_string'] = 'Sign=WXPay';
 
-			$string = 'appid='.$this->config->GetAppId().'&partnerid='.$order['partnerid'].'&prepayid='.$order['prepay_id'].'&package='.$order['package_string'].'&noncestr='.$order['nonce_str'].'&timestamp='.$order['time'];
+			$string = array();
+			$string['appid'] = $this->config->GetAppId();
+			$string['partnerid'] = $order['partnerid'];
+			$string['prepayid'] = $order['prepay_id'];
+			$string['package'] = $order['package_string'];
+			$string['noncestr'] = $order['nonce_str'];
+			$string['timestamp'] = $order['time'];
+			ksort($string);
+			$string = http_build_query($string);
 			if($order['sign_type'] == "MD5"){
 				$string = md5($string);
 			} else {