App.js

import {Platform, StyleSheet, Text, View } from 'react-native';
import React, {useEffect} from 'react';
import messaging from '@react-native-firebase/messaging';

const App = () => {
  useEffect(() => {
    Platform.OS === 'android' && getRegisterAndroid();
    getToken();
  }, []);

  // this method register the android device with fcm, For ios it automatically register when the app launched
  async function getRegisterAndroid() {
    let isDeviceRegistered =
      await messaging().registerDeviceForRemoteMessages();
    console.log('android device registered', isDeviceRegistered);
  }

  //both android and ios return unique device token
  async function getToken() {
    const token = await messaging().getToken();
    console.log('token', token);
  }

  return (
    <View style={{flex: 1, justifyContent: 'center', alignItems: 'center'}}>
      <Text>Notifee</Text>
    </View>
  );
};

export default App;

const styles = StyleSheet.create({});