code: func (w *Webhook) SendPayload(payload *Payload) error {
  	bs, err := json.Marshal(payload)
  	if err != nil {
  		return err
  	}
  
  	resp, err := http.Post("https://oapi.dingtalk.com/robot/send?access_token="+w.accessToken, "application/json", bytes.NewReader(bs))
  	if err != nil {
  		return err
  	}
  
  	bs, err = ioutil.ReadAll(resp.Body)
  	if err != nil {
  		return err
  	}
  
  	if resp.StatusCode != 200 {
  		return fmt.Errorf("%d: %s", resp.StatusCode, string(bs))
  	}
  
  	var result Response
  	err = json.Unmarshal(bs, &result)
  	if err != nil {
  		return err
  	}
  	if result.ErrorCode != 0 {
  		return fmt.Errorf("%d: %s", result.ErrorCode, result.ErrorMessage)
  	}
  
  	return nil
  }
docs: // SendPayload 发送消息