OneSignal is a free service for sending Push Notifications to users. Once your app is installed, you can send messages to all users or specific segments.
Do you need a REST API Key?
No
If you send notifications manually from the Dashboard — App ID alone is enough.
Yes
If you want automated server-triggered notifications — use the REST API Key server-side only, never in the app.
Setup Steps
1
Create a Firebase Project
Go to console.firebase.google.com → New Project → Android app → Package Name → Download google-services.json
Project Settings → Cloud Messaging → find Server Key & Sender ID
2
Create an App in OneSignal
onesignal.com → Sign in → New App → Platform: Google Android (FCM)
Paste FCM Server Key & Sender ID from Firebase
3
Get Your App ID
OneSignal → Settings → Keys & IDs
App ID → paste it in the field above ✓
REST API Key → server-side only
Paste the App ID & build your app
Paste the App ID above → after installing on a device, it appears in OneSignal Dashboard.
Important: The Package Name in Firebase must exactly match your app Package Name, otherwise notifications will not work.