public function getAvailableOptions($domain)
    {
        $domain = (string)$domain;
        if (!$domain)
            throw new BadMethodCallException('Parameter $domain is missing.');
        try {
            $r = $this->get('vps/' . $domain . '/availableOptions')->send();
        } catch (ClientErrorResponseException $e) {
            if ($e->getResponse()->getStatusCode() == '404' && json_decode($e->getResponse()->getBody())->message == "No options found")
                return "[]";
            else
                throw new VpsException($e->getMessage(), $e->getCode(), $e);
        } catch (\Exception $e) {
            throw new VpsException($e->getMessage(), $e->getCode(), $e);
        }
        return $r->getBody(true);
    }