我遇到了同样的问题.问题出在一行:

I was running into the same issue. The problem was in the line:

String serverKey = <get_server_key_from_firebase_console>;

此值应来自 Android 应用项目；在这种情况下，它将是我的通知客户端"而不是我的通知服务器".

This value should come from the Android app project; in this case it would be "My Notification Client" and not "My Notification Server".