public function toArray()
    {
        return [
            'message' => $this->content,
            'title' => $this->title,
            'timestamp' => $this->timestamp,
            'priority' => $this->priority,
            'url' => $this->url,
            'url_title' => $this->urlTitle,
            'sound' => $this->sound,
            'retry' => $this->retry,
            'expire' => $this->expire,
        ];
    }