public static function create($quantity, $productCode, $description, $amount, $vat, $currency = "EUR") {
        $item = new LineItem;
        $item->quantity = $quantity;
        $item->productCode = $productCode;
        $item->description = $description;
        $item->amount = $amount;
        $item->vat = $vat;
        $item->currency = $currency;
        return $item;
    }