Custom Post Type URL Structure Issues with Custom Post Type UI Plugin

Hello,

I’m using the Custom Post Type UI plugin to create a custom post type called ‘produktseiten’. Each ‘produktseiten’ post is assigned a parent post, and this is reflected in the URL which I have set up with a custom rewrite slug ‘c’.

The standard URL structure looks like this:

https://www.example.com/c/parent-post/post-name/

However, I want to remove the parent slug from the URL while maintaining the hierarchy within the WordPress structure (for breadcrumbs and other purposes). So, the URL should look like this:

https://www.example.com/c/post-name/

Here is the code that I’ve been using so far:

function remove_parent_slug($link, $post) {
    if ('produktseiten' == $post->post_type) {
        $link = home_url(user_trailingslashit("c/" . $post->post_name));
    }
    return $link;
}
add_filter('post_type_link', 'remove_parent_slug', 10, 2);

function fix_404_for_custom_post($query) {
    if (!is_admin() && $query->is_main_query() && 2 == count($query->query) && isset($query->query['page'])) {
        $query->set('post_type', array('post', 'produktseiten', 'page'));
    }
}
add_action('pre_get_posts', 'fix_404_for_custom_post');

Unfortunately, this results in a 404 error when I try to access the URL https://www.example.com/c/post-name/. It seems like WordPress cannot correctly find the post when the parent slug is missing.

Can anyone help solve this issue? Is there a setting or filter I can use in conjunction with the Custom Post Type UI plugin to achieve this URL structure?

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