code: def post_message(self, channel, text, **kwargs):
          
          if not channel.startswith('#'):
              channel = '#' + channel
          self.params.update({
              'channel': channel,
              'text':    text,
              })
          if kwargs:
              self.params.update(kwargs)
          return FromUrl('https://slack.com/api/chat.postMessage', self._requests)(data=self.params).post()
docs: https://api.slack.com/methods/chat.postMessage