正如 Frank van Puffelen 所说，没有办法发送到所有设备.您可以使用以下方式在应用程序端为每个人订阅一个主题:

As Frank van Puffelen said there isn't a way to send to all devices. What you could do is to subscribe everyone to a single topic in the app side using:

FirebaseMessaging.getInstance().subscribeToTopic("TopicName");

所以你的信息应该是这样的:

So your message would look like this:

  {
   "to"   : "/topics/TopicName",
   "data" : {
     "Nick" : "Mario",
     "body" : "great match!",
     "Room" : "PortugalVSDenmark"
   },
 }

主题是在 Firebase 服务器端自动创建的，但有时需要一段时间才能显示在 Firebase 下拉列表中.

The topic is automatically created in the Firebase server side, but sometimes it takes a while to show up in the Firebase drop down list.

单个主题的用户数不限.

The number of users in a single topic are unlimited.