https://blog.wongcw.com/2019/02/20/ios-12-2-beta-3%e7%99%bc%e5%b8%83%ef%bc%9agroup-facetime%e5%8a%9f%e8%83%bd%e9%87%8d%e6%96%b0%e4%b8%8a%e7%b7%9a/