code: def get_message_content(self, message_id, timeout=None):
          
          response = self._get(
              '/v2/bot/message/{message_id}/content'.format(message_id=message_id),
              stream=True, timeout=timeout
          )
  
          return Content(response)
docs: Call get content API.
  
          https://devdocs.line.me/en/#get-content
  
          Retrieve image, video, and audio data sent by users.
  
          :param str message_id: Message ID
          :param timeout: (optional) How long to wait for the server
              to send data before giving up, as a float,
              or a (connect timeout, read timeout) float tuple.
              Default is self.http_client.timeout
          :type timeout: float | tuple(float, float)
          :rtype: :py:class:`linebot.models.responses.Content`
          :return: Content instance