protected function getRequestHeaders($sendData = false)
    {
        $headers = [
            'Accept'     => 'application/json',
            'User-Agent' => $this->options->userAgent() . '/' . Client::VERSION,
        ];

        if ($sendData) {
            $headers['Content-Type'] = 'application/json;charset=utf-8';
        }

        return $headers;
    }