I have implemented adding a single user through android app but cannot register multiple users at the same time. Is there some java or android code which will allow me to regis
The Firebase client SDKs (for Android, iOS and Web) are meant to be used in end-user applications. They only allow you to register a single user at once, and that user is immediately signed in.
To register multiple users at once, consider using:
the Firebase Admin SDK, for which the Authentication functionality is only available in Node.js at the moment.
the auth:import command of the Firebase command line tools.