private function getResponse($endpoint, array $json) 
    {
        $result = null;
        // endpoint
        $uri = $this->config->getBaseUrl() . $endpoint;
        try {
            $response = $this->client->post(
                $uri, [
                'json' => $json,
                ]
            );
            // @todo $request->getHeader('content-type')
            if($response->getStatusCode() == '200') {
                $result = json_decode($response->getBody(), true);
            }else{
                echo 'ERROR: Status code ' . $response->getStatusCode();
            }
            // @todo check thrown exception
        } catch (\Exception $exception) {
            echo 'ERROR: ' . $exception->getMessage();
        }
        return $result;
    }