public function addDnc($id, $channel = 'email', $reason = Contacts::MANUAL, $channelId = null, $comments = 'via API') {

        return $this->makeRequest(
            'contacts/'.$id.'/dnc/'.$channel.'/add',
            array(
                'reason'    => $reason,
                'channelId' => $channelId,
                'comments'  => $comments,
            ),
            'POST'
        );
    }