OneSignal is one of the most popular web and mobile push notification service, used by ~half million developers worldwide.
OneSignal is available on multiple development platforms and the best thing is - it's FREE.
- React Native
- and many more...
If you are using WordPress then there is a plugin for you.
Setting up OneSignal wouldn't cost more than 15 minutes.
- Unlimited devices and unlimited notifications
- Provides real-time analytics
- Full API for custom integration
- A/B testing
- Can explore the data