code: def _call(self, endpoint, data=None):
          
          data = {} if data is None else data
          try:
              data['access_token'] = self.access_token()
              return self._request(endpoint, data)
          except AccessTokenExpired:
              self._cached_access_token = None
              data['access_token'] = self.access_token()
              return self._request(endpoint, data)
docs: Make an authorized API call to specified endpoint.
          :param str endpoint: API endpoint's relative URL, eg. `/account`.
          :param dict data: POST request data.
          :return: A dictionary or a string with response data.