To setup firebase api:

1. Create a project in https://console.firebase.google.com/
2. In General, create web application.
3. In Cloud Messaging, create web push certificates (will get vapidKey).
4. In Service accounts, generate private key
5. On the left menu, choose Build > Authentication, setup any users and sign-in method needed

To setup cloud google api:

1. Access to the created project on firebase api.
2. In Credentials, create credential > API Key, after that we will get APIKey
3. In Credentials, create credential > OAuth Client Id (will get the client Id and secrets)
   • to test with postman, add this "Authorized redirect URIs" https://www.getpostman.com/oauth2/callback
   • to test with playround, add this "Authorized redirect URIs" https://developers.google.com/oauthplayground

Try playround:

1. Access the the playround: https://developers.google.com/oauthplayground
2. Step 1, key in https://www.googleapis.com/auth/firebase.messaging then Authorize APIs
3. Step 2, Exchange authorization code for tokens (will get Refresh token and Access token)
4. Step 3, try to send message
   • http method: POST
   • key in https://fcm.googleapis.com/v1/projects/{your-project-id}/messages:send
   • Add header: Content-Type = application/json, Authorization = Bearer {your-Access-token}
   • Enter request body, token is the device FCM token that will receive the message

{ "message": { "token": "fIuVH019sy4fSYYXfPkJr8:APA91bG-8fKv3qY9_rOdCVew9s3PHW9gCczicQyg-fByEyPy483oKVIAbzgawSgXXwwZ1ou98PvbhXifpgC3oDZLkj_RqFZvN1Xeqd30FfKa2aPT3TcMgq2PHVPHQ9STfNtNwoLhe8zo", "notification": { "title": "Test title", "body": "Test body" } } } 

To make the api work on the backend, click on the setting icon on the top right of playground