is there anyone who uses node to access Audio SMS to customize the SMS interface of exemption from examination?

request.post(
     {
          url:"https://sms.aodao.com.cn/api/api.php",
          form:  {
                a:"diysms",
                agv: "{"name": "","inform_con": "hjb","mobile": ""+phone+"","content": ":"+code+"hjb","typeid":"1","appid": ""+appid+"","appkey": ""+appkey+"","token": "12345678","time": ""+str+"","sign": ""+sign+"","sendtime": ""+str+""}"
                 }
      },
      function(error, response, body) {
           res.json({
                 "result": "0",
                 "info": JSON.parse(body)
                })
       }
 )

is completely in accordance with the API document, but it always returns a signature verification failure. What exactly is the reason?