Add custom query var to exists WordPress page get 404

I have created a WordPress page with name: shows. Now I want to add custom query var to that page’s URL but get 404 error.

example.com/shows/test-var/

function custom_rewrite_tag() {
    add_rewrite_tag('%animation%', '([^&]+)');
}
add_action('init', 'custom_rewrite_tag', 10, 0);

function custom_rewrite_rule() {
    add_rewrite_rule('^shows/([^/]*)/([^/]*)/?', 'index.php?pagename=$matches[1]&animation=$matches[2]', 'top');
    flush_rewrite_rules();
}
add_action('init', 'custom_rewrite_rule', 10, 0);

Can everyone help me? Thanks a lot.