请求URL：

https://api.mch.weixin.qq.com/pay/combinedorder

请求参数：

<xml>

<combine_appid>wxf64188de8b42aed5</combine_appid>

<combine_mch_id>1565784021</combine_mch_id>

<combine_openid>ovzga431UhrB1JQbZ7f2UmMW-U0g</combine_openid>

<combine_out_trade_no>5e1b4a124b2e00183846dac1</combine_out_trade_no>

<nonce_str>1690250507</nonce_str>

<notify_url>http://shop.ueecai.com/api/order/CommitOrder</notify_url>

<sign>904760fe8c45fa12d204b1d480a80412b439385871be7da4bf08a5ab031b6e78</sign>

<sign_type>HMAC-SHA256</sign_type>

<spbill_create_ip>139.196.145.248</spbill_create_ip>

<sub_order_list>{"order_list":[{"appid":"wxf64188de8b42aed5","mch_id":"1565784021","body":"test1","out_trade_no":"5e1b4a124b2e00183846dac2","fee_type":"CNY","total_fee":724998},{"appid":"wxf64188de8b42aed5","mch_id":"1565784021","body":"test1","out_trade_no":"5e1b4a124b2e00183846dac3","fee_type":"CNY","total_fee":152664}],"order_num":2}</sub_order_list>

<trade_type>JSAPI</trade_type>

</xml>

返回参数：

<xml><return_code><![CDATA[FAIL]]></return_code>

<return_msg><![CDATA[System Error]]></return_msg>

</xml>

麻烦看一下这个问题是出在什么地方