add_submenu_page returns null

Question

After creating a parent admin menu item, which works fine, I fail to add a submenu page. Trying to var_dump the return value of add_submenu_page() I get 'null'.

My functions are:

    /**
     * Register the admin menu page
     * 
     * @since   1.0.0
     */
    public function add_admin_menu() {
        add_menu_page( 'WPQuotes', 'WPQuotes', 'manage_options', 'wp-quotes-plugin', 'wpq_admin_settings_page_main', 'dashicons-networking' );
        add_submenu_page( 'wp-quotes-plugin', 'New WPQ Form', 'New WPQ Form', 'manage-options', 'wpq-new-form', 'wpq_admin_settings_page_new_form');
    }

    public function run_all(){
        add_action( 'admin_menu', array($this, 'add_admin_menu'), 10 );
    }

Answer 1

Your code is correct but just you have called wrong capability in add_submenu_page.

You just need to replace this 'manage_options' instead of 'manage-options'. And please check it. It's works.

Reference: https://developer.wordpress.org/reference/functions/add_submenu_page/