hotspotbilling.phpnuxbill/system/controllers/logout.php

<?php
/**
* PHP Mikrotik Billing (https://github.com/hotspotbilling/phpnuxbill/)
**/
run_hook('customer_logout'); #HOOK
if (session_status() == PHP_SESSION_NONE) session_start();
session_destroy();
header('location: index.php');