docs: async def _send(self,
                      request: Request,
                      content: Dict[Text, Any],
                      stack: Stack):
          """
          Actually proceed to sending the message to the Facebook API.
          """
  
          msg = {
              'recipient': {
                  'id': request.conversation.fbid,
              },
              'message': content,
          }
  
          if stack and stack.has_layer(MessagingType):
              mt = stack.get_layer(MessagingType)
          else:
              mt = MessagingType(response=True)
  
          msg.update(mt.serialize())
          msg_json = ujson.dumps(msg)
  
          headers = {
              'content-type': 'application/json',
          }
  
          params = {
              'access_token': self._access_token(request),
          }
  
          post = self.session.post(
              MESSAGES_ENDPOINT,
              params=params,
              data=msg_json,
              headers=headers,
          )
  
          logger.debug('Sending: %s', msg_json)
  
          async with post as r:
              await self._handle_fb_response(r)