public function listen() {
        $body = file_get_contents('php://input');
        $message = json_decode($body, true);
        if (empty($message)) {
            return;
        }
        if (!isset($message['Message'])) {
            return;
        }
        $response = json_decode($message['Message'], true);
        if (!isset($response['ObjectType']) || !isset($response['ObjectId'])) {
            return;
        }

        $opts = $this->module->getActingOpts();
        $opts['ipn_verified'] = true;
        $this->module->updateActingOpts($opts);

        switch ($response['ObjectType']) {
            case EventNames::CHARGE:
                $orderId = $this->getOrderIdFromChargeId($response['ObjectId']);
                if ($orderId !== null) {
                    $order = new Models\OrderMeta($orderId);
                    if (!in_array($response['NotificationId'], $order->getIpnNotificationIds(), true)) {
                        $order->updateNotificationIds($response['NotificationId']);
                        $this->updateChargeState($order);
                    }
                }
                break;
            case EventNames::REFUND:
                $orderId = $this->getOrderIdFromRefundId($response['ObjectId']);
                if ($orderId !== null) {
                    $order = new Models\OrderMeta($orderId);
                    if (!in_array($response['NotificationId'], $order->getIpnNotificationIds(), true)) {
                        $order->updateNotificationIds($response['NotificationId']);
                        $this->updateRefundState($order);
                    }
                }
                break;
        }
    }