Dynamic dependent select box getting null value

add this two hooks at the end of your ajax-cities.php file

add_action('wp_ajax_my_action', 'my_action' );
add_action('wp_ajax_nopriv_my_action', 'my_action');

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)