Custom rewrite

Custom rewrite
I want create custom page and subpages with Custom rewrite

I have in page in wordpress – “sing” https://127.0.0.1/wordpress/sing/

I creat custom rewrite
add_action(‘generate_rewrite_rules’, ‘work_list’);
function work_list($wp_rewrite) {
$newrules = array();
$newrules[‘sing/music/’] = ‘index.php?clients=okay])’;
$wp_rewrite->rules = $newrules + $wp_rewrite->rules;
}
whem am in page in firebug say this page is 404