Пример подключения собственного класса доставки

<?php
if(!class_exists('msDeliveryInterface')) {
    require_once dirname(dirname(dirname(__FILE__))) . '/model/minishop2/msdeliveryhandler.class.php';
}

class msDeliveryHandlerMsk extends msDeliveryHandler implements msDeliveryInterface{

    public function getCost(msOrderInterface $order, msDelivery $delivery, $cost = 0) {

        $freedeliverysumm = $modx->getOption('free_delivery');
        $cart = $order->ms2->cart->status();
        $cart_cost = $cart['total_cost'];

        if($cart_cost > $freedeliverysumm){
            return $cost;
        }else{
            $delivery_cost = parent::getCost($order, $delivery, $cost);
            return $delivery_cost;
        }
    }
}