docs: async def call(self, method, **params):
          """
          Call an Slack Web API method
  
          :param method: Slack Web API method to call
          :param params: {str: object} parameters to method
          :return: dict()
          """
          url = self.SLACK_RPC_PREFIX + method
          data = FormData()
          data.add_fields(MultiDict(token=self.bot_token, charset='utf-8', **params))
          response_body = await self.request(
              method='POST',
              url=url,
              data=data
          )
          if 'warning' in response_body:
              logger.warning(f'Warnings received from API call {method}: {response_body["warning"]}')
          if 'ok' not in response_body:
              logger.error(f'No ok marker in slack API call {method} {params} => {response_body}')
              raise SlackCallException('There is no ok marker, ... strange', method=method)
          if not response_body['ok']:
              logger.error(f'Slack API call failed {method} {params} => {response_body}')
              raise SlackCallException(f'No OK response returned', method=method)
          return response_body