Not working for custom post type

Hey,
ive created a custom post type with the slug “xyz”.

Ive added your code from here:
https://www.ads-software.com/support/topic/use-with-custom-post-type-1/
and insert the slug.

But its not working?!

//using a filter hook
add_filter(‘USC_allowed_post_types’,’usc_filter_post_types’);
function usc_filter_post_types($types){
//to add a custom post type
$types[] = ‘xyz’;

//to remove a post type
if(($key = array_search(‘post’, $types)) !== false) {
unset($types[$key]);
}
}