Creating a quiz Android app supporting real time players

I am developing an android quizzing application and want to add a realtime multiplayer feature.
Till now I have seen Google play services, Service providers like ShepHertz, Photon but all of them are paid.

As the application is for learning purposes, I am looking for a solution that is free to use and explore. Are there such service providers providing facilities like Leaderboard/Creation of room for a game etc for free?

Kindly share some resources if there is a way to achieve this without the help of such platforms.

PS- I am an Android app developer and naive in Game development.