For me it was somewhat annoying to find the simplest path to implement remote push notifications (PN) badges (ios) on background React Native apps.

I suppose you already have set up your PNs based on e.g. firebase.

We don't use the following approaches

• the server controlled way setting apns.payload.aps.badge (It is annoying to handle that logic for each user in the backend)
• the NotificationService.swift and UserDefaults approach (it is ok to write Swift, but it is still annoying to use XCode)

Ok let's go:

• Make sure to request badge permissions, this took me quite a while to check that this is required, otherwise you'll receive PNs but no badge will ever appear anywhere - there won't even be the badge slider available in your app settings.

import { requestNotifications } from 'react-native-permissions'
...
React.useEffect(() => {
   requestNotifications(['alert', 'badge'])
},[])

• Create a CloseStatePseudoApp to make sure that firebaseMessagings background messages run even if the app is in closed state

const MainApp  = () => ...

const ClosedStatePseudoApp = () => {
    React.useEffect(() => {
        SplashScreen.hide();
    }, []);

    return null;
};

AppRegistry.registerComponent('YourAppname', (props) =>
    props?.isHeadless ? ClosedStatePseudoApp() : MainApp()
);

• Install @notifee/react-native (podinstall)

• Set up firebaseMessagingService.setBackgroundMessageHandler somewhere in a effect hook, and make sure to call the notifee.incrementBadgeCount() method
  

import notifee from '@notifee/react-native';
import messaging from '@react-native-firebase/messaging';
const messagingService = messaging();

React.useEffect(() => {
   messagingService.setBackgroundMessageHandler(async (message:    RemoteMessage) => {
        console.log('messagingService.backgroundMessage', message);
        await notifee.incrementBadgeCount();
    });
},[])

• To reset the badge count to 0, once the app went foreground, use react natives AppState and notifee to do so

import { AppState } from 'react-native';
import notifee from '@notifee/react-native';

AppState.addEventListener('change', (nextAppState) => {
    switch (nextAppState) {
        case 'active': {
            notifee.setBadgeCount(0);
        }
        default:
            return;
    }
});

Done.