Hi Darshan,
Approach is same as for other platforms. Here in this case your reactive web application is supposed to be used by staff user or admin user. They have UI to send notifications to users.
So for notifications on mobile application, you need to use some notification service. Lets take example of Firebase push notifications. So in that case you need to register your project on Firebase console, Then from web application when you send any notification it will go through Firebase. Same in mobile application you need to add Firebase plugin to receive the push notifications.
You can achieve same functionality by other notification providers as well. Its depend on your requirement.