Custom EndPoint not working when strip child category in URL

Question

I have created a custom endpoint for Download page with Permalink setting:

/%category%/%postname%/

The URL as below:

domain.com/top-category/child-category/post-slug/download

function themes_download() {
    add_rewrite_endpoint( 'download', EP_PERMALINK | EP_PAGES );
   
}
add_action( 'init', 'themes_download' );

function themes_download_template() {
    global $wp_query;
    $dl_val = intval( get_query_var( 'download' ) );

    // if this is not a request for play or a singular object then bail
    if ( ! isset( $wp_query->query_vars['download'] ) || ! is_singular() )
        return;
    //Return 404 if no download link
    $dl_id = intval( get_query_var( 'download' ) );
    $dl_url = get_post_meta(get_the_ID(), 'repeatable_fields', true);
    if($dl_val!=0 && empty($dl_url[$dl_id-1])) {
            $wp_query->set_404();
            status_header( 404 );
            get_template_part( 404 );
            exit();
    }

    // include custom template
    include get_template_directory().'/vietrick/download.php';
    exit;
}
add_action( 'template_redirect', 'themes_download_template' );

However, I also want to remove the child category from URL with following code:

function remove_child_categories_from_permalinks( $category ) {
    while ( $category->parent ) {
        $category = get_term( $category->parent, 'category' );
    }
    return $category;
}
add_filter( 'post_link_category', 'remove_child_categories_from_permalinks', 999 );

The code work for:

• domain.com/top-category/post-slug/
• domain.com/top-category/child-category/post-slug/download

But the custom endpoint does not work for:

• domain.com/top-category/post-slug/download

Anyone has any idea?

Answer 1

Disable the Canonical redirect will keep the code work:

function disable_canonical_redirect_for_download_page( $redirect ) {
    if ( isset( $wp_query->query_vars['download'] ) || is_singular() ) {
            $redirect = false;
    }

    return $redirect;
}
add_filter( 'redirect_canonical', 'disable_canonical_redirect_for_download_page' );