public static function init() {
        // set priority to 20 so inventory is updated last
        add_action('usces_action_reg_orderdata', [get_class(), 'updateInventoryOnPurchase'], 20, 1);
        add_action('usces_action_reg_ordercart_row', [get_class(), 'addGroupItemsToOrderCart'], 10, 4);
    }