和官网demo一模一样的格式

<xml>

<mch_appid>wxf5ebee3eedc05935</mch_appid>

<mchid>1567722331</mchid>

<nonce_str>gtpuhlgtd9ks7csmta2lkknb5e169hf4</nonce_str>

<check_name>NO_CHECK</check_name>

<amount>1</amount>

<desc>ceshi</desc>

<partner_trade_no>abc1616215394</partner_trade_no>

<openid>oE6PV0ZRU2yPii3TA_e7SiJNJ-uw</openid>

<spbill_create_ip>58.57.167.158</spbill_create_ip>

<sign>0CD782C37CCA25615C353478158FCBA9</sign>

</xml>

但是始终报错：

 ["return_code"]=>
  string(7) "SUCCESS"
  ["return_msg"]=>
  string(15) "XML解析错误"
  ["result_code"]=>
  string(4) "FAIL"
  ["err_code"]=>
  string(9) "XML_ERROR"
  ["err_code_des"]=>
  string(15) "XML解析错误"