code: func (r *Response) PassThreadToInbox() error {
  	p := passThreadControl{
  		Recipient:   r.to,
  		TargetAppID: InboxPageID,
  		Metadata:    "Passing to inbox secondary app",
  	}
  
  	data, err := json.Marshal(p)
  	if err != nil {
  		return err
  	}
  
  	req, err := http.NewRequest("POST", ThreadControlURL, bytes.NewBuffer(data))
  	if err != nil {
  		return err
  	}
  
  	req.Header.Set("Content-Type", "application/json")
  	req.URL.RawQuery = "access_token=" + r.token
  
  	resp, err := http.DefaultClient.Do(req)
  	if err != nil {
  		return err
  	}
  	defer resp.Body.Close()
  
  	return checkFacebookError(resp.Body)
  }
docs: // PassThreadToInbox Uses Messenger Handover Protocol for live inbox
  // https://developers.facebook.com/docs/messenger-platform/handover-protocol/#inbox