[notifee] no background event handler has been set. Set a handler via the "onBackgroundEvent" method.

This warning appears when I launch a test notification with FCM. The notification appears twice in background mode (I don’t know why twice), and once in foreground mode.

This warning only appears in background mode.

index.js

import { registerRootComponent } from 'expo';
import Notification from '@/configs/Notification';
import notifee from '@notifee/react-native';
import messaging from '@react-native-firebase/messaging';

import App from './App';

Notification.getFCMToken();


messaging().setBackgroundMessageHandler(async (remoteMessage) => {
	notifee.displayNotification({
		title: remoteMessage.notification.title,
		body: remoteMessage.notification.body,
		android: {
			channelId: 'default',
		}
	});
});

// registerRootComponent calls AppRegistry.registerComponent('main', () => App);
// It also ensures that whether you load the app in Expo Go or in a native build,
// the environment is set up appropriately
registerRootComponent(App);

Notification.getFCMTOken

	getFCMToken: async () => {
		const hasPermission = await messaging().hasPermission();
		if (!hasPermission) {
			await messaging().requestPermission();
		}

		await messaging().registerDeviceForRemoteMessages();
	
		const token = await messaging().getToken();
	
		if (token) {
			userDetails = await firestore()
				.collection('users')
				.doc(auth().currentUser.uid)
				.get();
			
			if (userDetails.exists) {
				userToken = userDetails.data().fcmToken;
				
				if (userToken != token) {
					firestore()
						.collection('users')
						.doc(auth().currentUser.uid)
						.update({
							fcmToken: token,
						});
				}
			}
		}
	},

App.js

import React from 'react';
import { store } from "./app/redux/store";
import { Provider } from "react-redux";
import AppNavigator from './app/navigation/AppNavigator';
import { SafeAreaView } from 'react-native';
import { StatusBar } from 'expo-status-bar';
import notifee from '@notifee/react-native';
import messaging from '@react-native-firebase/messaging';

export default function App() {
  React.useEffect(() => {
    return messaging().onMessage(async (remoteMessage) => {
      notifee.displayNotification({
        title: remoteMessage.notification.title,
        body: remoteMessage.notification.body,
        android: {
          channelId: 'default',
        }
      });
    });
  }, []);

  return (
    <SafeAreaView style={{
      flex: 1,
    }}>

      <StatusBar
        style="light-content"
        animated={true}
        translucent={true}
      />

      <Provider store={store}>
        <AppNavigator />
      </Provider>
    </SafeAreaView>
  );
}