<?php

require_once '../../../wp-load.php';
require_once '../../../wp-config.php';
$obj_sage = new SagePayGateway();
if (isset($_SESSION['transaction']['VPSTxId'])) {
    $obj_sage->process_completed();
} else {
    $obj_sage->process_incompleted();
}
<?php

require_once '../../../wp-load.php';
require_once '../../../wp-config.php';
$data['MD'] = $_POST['MD'];
$data['PaRes'] = $_POST['PARes'];
$secure = new SecureAuth($data);
$obj_sage = new SagePayGateway();
if ($secure->status == 'success') {
    $obj_sage->process_completed();
} else {
    $obj_sage->process_incompleted($secure->error);
}