protected function addLineItems(array $params, array $options)
    {
        $currency = Arr::get($options, 'currency', $this->gateway->getCurrency());

        $items = [];
        $itemsTotal = 0;
        foreach (Arr::get($options, 'line_items', []) as $item) {
            $items[] = [
                'name'        => $item['name'],
                'description' => Arr::get($item, 'description'),
                'quantity'    => $item['quantity'],
                'price'       => $this->gateway->amount($item['unit_price']),
                'sku'         => Arr::get($item, 'sku'),
                'currency'    => $currency,
            ];
            $itemsTotal += $item['unit_price'] * $item['quantity'];
        }

        if (!empty($items)) {
            $params['transactions'][0]['item_list']['items'] = $items;
            $params['transactions'][0]['amount']['details']['subtotal'] = $this->gateway->amount($itemsTotal);
        }

        return $params;
    }