Is there a way to send a message to an entire application instead of a list of devices / topic outside the Firebase console?
Inside the console you can accomplish this like so:
But if I'm using their API, I can't find a way to send the message to the app.
I have found a workaround (subscribing every app to the same topic) that works perfectly, but I would prefer the app option.
Once you subscribe users of your app to a topic, every user gets the message sent to that topic.
You can't send message to the entire users of your app with API without a topic. It only works in Firebase Console. See this explanation: FCM (Firebase Cloud Messaging) how to send to all Phones?