mailjet-8.x-2.7/modules/mailjet_event/src/Controller/EventCallbackController.php

<?php

/**
 * @file
 * Contains \Drupal\mailjet_event\Controller\EventCallbackController.
 */

namespace Drupal\mailjet_event\Controller;

use Drupal\Core\Controller\ControllerBase;

class EventCallbackController extends ControllerBase
{

    public function callback()
    {
        $build = [];
        _mailjet_event_alter_callback();
        return $build;
    }

}