docs: def post_chat_message(self, merchant_id, channel_id, message):
          """post a chat message
  
          Arguments:
              channel_id:
                  Scan token
          """
  
          return self.do_req('POST',
                             self.base_url + '/chat/v1/merchant/%s/channel/%s/message/' % (merchant_id, channel_id),
                             message)