public static function getVisibilityIndexByApi($url = false, $db = false)
    {
        self::guardApiKey();
        self::guardApiCredits();

        $url = parent::getUrl($url);
        $domain = static::getDomainFromUrl($url);
        $database = static::getValidDatabase($db);

        $dataUrl = sprintf(Config\Services::SISTRIX_API_VI_URL, Config\ApiKeys::getSistrixApiAccessKey(), urlencode($domain), $database);

        $json = static::_getPage($dataUrl);

        if(empty($json)) {
            return parent::noDataDefaultValue();
        }

        $json_decoded = (Helper\Json::decode($json, true));
        if (!isset($json_decoded['answer'][0]['sichtbarkeitsindex'][0]['value'])) {
            return parent::noDataDefaultValue();
        }
        return $json_decoded['answer'][0]['sichtbarkeitsindex'][0]['value'];
    }