public static function createClient($apiKey, $product = null)
    {
        Guard::uuid(
            static::apiKeyToUuid($apiKey),
            'ING API key is invalid: '.$apiKey
        );

        if (!static::validPHPVersion()) {
            throw new \Exception('Minimum required PHP version must be '.MIN_PHP_VERSION.' or above.');
        }

        return new Client(
            strtr(
                static::getEndpoint($product),
                ['{version}' => self::API_VERSION]
            ),
            Request::init()
                ->authenticateWith($apiKey, '')
                ->addHeaders([
                    'User-Agent' => 'ing-php/'.self::CLIENT_VERSION,
                    'X-PHP-Version' => PHP_VERSION
                ])
        );
    }