private static function _getConnectParam($paramName, $params = null)
    {
        $oauthParam = ($params && array_key_exists($paramName, $params))
        ? $params[$paramName] : null;

        if ($oauthParam === null) {
            $funcName = 'get' . Util\Util::toCamelCase($paramName, true);
            $oauthParam = Sumup::{$funcName}();
        }

        if ($oauthParam === null) {
            $msg = 'No '.$paramName.' provided. You can find your '. $paramName
            . ' in your Sumup dashboard at '
            . 'https://me.sumup.com/developers, '
            . 'after registering your account as a platform. See '
            . 'https://sumupus.desk.com/ for details, '
            . 'or email support@sumup.com if you have any questions.';
            throw new Error\AuthenticationError($msg);
        }

        return $oauthParam;
    }