Hello i found this code and I modified a litle, but i have a problem with it.

I want the link of the attachment page to be something like this 

    [post-permalink]/[gallery]/[postid]   1234/ .. /1253/ 

I tried this, the URL is like I want to be but gives me a 404 error:

    function wpd_attachment_link( $link, $post_id ){
    $post = get_post( $post_id );
    return get_permalink() . 'galery/' . $post->ID ;
    }
    add_filter( 'attachment_link', 'wpd_attachment_link', 20, 2 );


How to do that?