退款返回参数：<xml><return_code><![CDATA[FAIL]]></return_code> <return_msg><![CDATA[]]></return_msg> </xml> 没有失败的原因返回

请求参数：<xml><appid>wxbd9a60fc9cfea6c7</appid><mch_id>1487080802</mch_id><nonce_str>efb9947bfbf6450495d41f8681faa9c7</nonce_str><sign_type>HMAC-SHA256</sign_type><sign><![CDATA[5D9BCEB948275314EAEDE70CC7B2192D]]></sign><transaction_id>4200000517202002284418529664</transaction_id><out_refund_no>rd200001200200011</out_refund_no><total_fee>1</total_fee><refund_fee>1</refund_fee><refund_desc>拼团失败</refund_desc><refund_account>REFUND_SOURCE_UNSETTLED_FUNDS</refund_account></xml>