app\Billy::createInvoice PHP Method

    public static function createInvoice($params)
    {
        $realParams = array('invoice' => array('organizationId' => 'ACx42GkURdCdQFFweX7VDQ', 'contactId' => $params['contactId'], 'paymentTermsDays' => 8, 'currencyId' => $params['Currency'], 'entryDate' => Carbon::now()->format('Y-m-d'), 'lines' => array()));
        foreach ($params['ProductLines'] as $productLine) {
            $realParams['invoice']['lines'][] = array('unitPrice' => $productLine['BaseAmountValue'], 'productId' => 'Ccx9WbbORtGTQtRX48Sdtg', 'description' => $productLine['Description']);
        }
        $res = self::request("POST", "/invoices", $realParams);
        return $res;
    }