public function execute()
    {
        parent::execute();

        $xml = new DOMDocument();
        $hpsTransaction = $xml->createElement('hps:Transaction');
        $hpsCreditVoid = $xml->createElement('hps:CreditVoid');
        $hpsCreditVoid->appendChild($xml->createElement('hps:GatewayTxnId', $this->transactionId));
        $hpsTransaction->appendChild($hpsCreditVoid);

        return $this->service->_submitTransaction($hpsTransaction, 'CreditVoid', $this->clientTransactionId);
    }