Before going to configure firebase push notification on ios and android platform you need to configure your project on firebase console.

You have to create project and ios and android application on firebase console.

Add bundle identifier of ios and application packages id of Android project.

Please follow all the steps which are mentioned on firebase console for both iOS and Android application.

Download google-service.json file for Android

Download Google-service-info.plist file for iOS

On Admin Panel open menu Settings -> Settings and put Firebase Cloud Messaging Key