预签约的时候 return_msg = '不识别的参数contract_code'

<xml>
  <appid>*********</appid>
  <mch_id>*********</mch_id>
  <plan_id>*******</plan_id>
  <contract_code>20200311000000002T</contract_code>
  <request_serial>1583922071</request_serial>
  <contract_display_account>test</contract_display_account>
  <notify_url>**********</notify_url>
  <version>1.0</version>
  <timestamp>1583922090</timestamp>
  <sign>***************</sign>
</xml>