code: def nack(self, id, transaction=None, receipt=None):
          
          assert id is not None, "'id' is required"
          headers = {HDR_ID: id}
          if transaction:
              headers[HDR_TRANSACTION] = transaction
          if receipt:
              headers[HDR_RECEIPT] = receipt
          self.send_frame(CMD_NACK, headers)
docs: Let the server know that a message was not consumed.
  
          :param str id: the unique id of the message to nack
          :param str transaction: include this nack in a named transaction