When I use this

$create_user = wp_create_user('username', 'password', 'email');
    
    $new_user = new WP_User($create_user);

    $new_user -> set_role('user_role');

on my function file of theme. It's working fine. But When I use this on plugin file. It's showing fetal error. How should use this ? There is any hook for plugin ? Thanks