protected function addTransaction()
    {
        /* @var $model \gplcart\core\models\Transaction */
        $model = gplcart_instance_model('Transaction');

        $transaction = array(
            'total' => $this->data_order['total'],
            'order_id' => $this->data_order['order_id'],
            'currency' => $this->data_order['currency'],
            'payment_method' => $this->data_order['payment'],
            'gateway_transaction_id' => $this->response->getTransactionReference()
        );

        return $model->add($transaction);
    }