public function getSubscribers($groupId, $type = null, $params = [])
    {
        $endpoint = $this->endpoint . '/' . $groupId . '/subscribers';

        if ($type !== null) {
            $endpoint .=  '/' . $type;
        }

        $params = array_merge($this->prepareParams(), $params);

        $response = $this->restClient->get($endpoint, $params);

        return $response['body'];
    }