payment_callback.php

<?php

$startTime = microtime(true);
$fileDir = dirname(__FILE__);

require($fileDir . '/library/XenForo/Autoloader.php');
XenForo_Autoloader::getInstance()->setupAutoloader($fileDir . '/library');

XenForo_Application::initialize($fileDir . '/library', $fileDir);
XenForo_Application::set('page_start_time', $startTime);

$deps = new XenForo_Dependencies_Public();
$deps->preLoadData();

$response = new Zend_Controller_Response_Http();
$processor = new XenForo_UserUpgradeProcessor_PayPal();
$processor->initCallbackHandling(new Zend_Controller_Request_Http());

$logExtra = array();
$logMessage = false;

try
{
    if (!$processor->validateRequest($logMessage))
    {
        $logType = 'error';

        $response->setHttpResponseCode(500);
    }
    else if (!$processor->validatePreConditions($logMessage))
    {
        $logType = 'error';
    }
    else
    {
        $logType = 'info';
        $logMessage = $processor->processTransaction();
    }

    if (is_array($logMessage))
    {
        $temp = $logMessage;
        list($logType, $logMessage) = $temp;
    }
}
catch (Exception $e)
{
    $response->setHttpResponseCode(500);
    XenForo_Error::logException($e);

    $logType = 'error';
    $logMessage = 'Exception: ' . $e->getMessage();
    $logExtra['_e'] = $e;
}

$processor->log($logType, $logMessage, $logExtra);

$response->setBody(htmlspecialchars($logMessage));
$response->sendResponse();