public function request(Config $config, ContentItems $contentItems)
    {
        $this->config = $config;

        $options = [
            'headers' => [
                'X-Watson-Authorization-Token' => $this->getAuthToken(),
                'X-Watson-Learning-Opt-Out' => $this->config->optOutOfLogging,
                'Content-Type' => 'application/json',
                'Accept' => 'application/json',
                'Accept-Language' => 'en'
            ],
            'body' => $contentItems->getContentItemsContainerJson()
        ];

        $response = $this->client->request(
            'POST',
            $config->getApiUrl(),
            $options
        );
        return json_decode($response->getBody());
    }