public function isSuccessful()
    {
        // As per appendix F, 000 means the message was processed correctly
        if ((string) $this->data->Status->statusCode !== '000'
            || ($this->hasTransaction()
                && (string) $this->data->Payment->TxnList->Txn->approved !== 'Yes')) {
            return false;
        }

        return true;
    }