public function getRates($shopSum, $paymentMethod = '', $culture = null)
    {
        if (null === $culture) {
            $culture = $this->culture;
        }

        $response = $this->sendRequest(
            $this->serviceBaseUrl . 'GetRates',
            [
                'MerchantLogin' => $this->auth->getMerchantLogin(),
                'IncCurrLabel'  => $paymentMethod,
                'OutSum'        => $shopSum,
                'Language'      => $culture
            ],
            $this->requestMethod
        );

        $sxe = simplexml_load_string($response);
        $this->parseError($sxe);

        if (!$sxe->Groups->Group) {
            return [];
        }
        $groups = [];
        foreach ($sxe->Groups->Group as $i => $group) {
            $items = [];
            foreach ($group->Items->Currency as $item) {
                $clientSum = (double)$item->Rate->attributes()->IncSum;
                $item = (array)$item;
                $items[] = $item['@attributes'] + ['ClientSum' => $clientSum];
            }
            $groups[] = [
                'Code'        => (string)$group->attributes()->Code,
                'Description' => (string)$group->attributes()->Description,
                'Items'       => $items,
            ];
        }

        return $groups;
    }