private function sendRaw($slackMsg)
    {
        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $this->endpoint);
        curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
        curl_setopt($ch, CURLOPT_POSTFIELDS, $slackMsg);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt(
            $ch,
            CURLOPT_HTTPHEADER,
            array(
                'Content-Type: application/json',
                'Content-Length: ' . strlen($slackMsg)
            )
        );
        curl_exec($ch);
    }