Send topic-based web push notifications using FCM and Ionic 4. Broadcast messages to millions of users with just a few simple cloud functions https://angularfirebase.com/lessons/fcm-topic-notifications-angularfire-and-callable-functions/
– FCM https://firebase.google.com/docs/cloud-messaging/
– Ionic 4 https://blog.ionicframework.com/announcing-ionic-4-beta/