Decline to acknowldge the given message.

        This will cause the message to be re-delivered to the subscription.

def nack(self):
        """Decline to acknowldge the given message.

        This will cause the message to be re-delivered to the subscription.
        """
        self._request_queue.put(
            requests.NackRequest(ack_id=self._ack_id, byte_size=self.size)
        )