You should use ‘post_type_link’ hook
and register post type ‘project’ with (‘with_front’ => true) parameters
'rewrite' => array('slug' => $slug, "with_front" => true),
==================================or=====================================
add_rewrite_rule('^project/([0-9a-z]+)/?$', 'index.php?project=$matches[1]', 'top');
====================================================================
function post_type_link_hook($link, $post) {
add_rewrite_tag('%url_id%','([^&]+)');
if ('projects' == get_post_type($post)) {
$urlId = get_post_meta($post->ID, 'url_id', true);
//Lets go to get the parent cartoon-series name
return str_replace('%url_id%', $urlId, $link);
}
return $link;
}
add_filter('post_type_link', 'post_type_link_hook', 10, 2);