Properly redirect to logout from third-party site?

Hi – I have a third-party service that’s hosting a subdomain of my WP site. The WP site is BookTrib.com, and the subdomain hosted elsewhere is video.BookTrib.com.

The third-party site, which isn’t WP, obviously can’t generate the correct logout URL with nonce, so I’m trying to create a logout page that redirects to the correct logout with nonce.

My current code for the second logout page, which the third party logout link goes to, is:

<?php
require_once(‘wp-config.php’);
wp_redirect(wp_logout_url(“/”));
?>

However, this still results in the “Are you sure…” page. I’m not entirely sure what the problem is here – any ideas?

Alternatively, what’s the most correct way of removing the “Are you sure..” notification? Thanks all.