Android online multiplayer
Google Play has nothing to do the multiplayer part, it's just a platform which hosts your .apk file and gives the users access to download your game. For [online] mobile multiplayer you have to have a dedicated server to which the players can connect, apart from the Play Store. Even if your game has a bigger file size than 100mb(?) you have to store the content on a server of yours and handle the content download inside your game.
Anyway, to create a multiplayer game inside unreal for mobile is the exact same process as for any other platform -not steam but unreals built in methods- (thats the nice thing about a multi platform capable engine like unreal) and to set up a dedicated server for mobile is also the same as for pc or anything else.
Obviously your gamelogic has to be built for multiplayer (replications, server has authority, validation checks and so on).
You can either host a dedicated server by yourself (e.g. your pc for testing) or use a service like amazons EC2 (+gamelift) and upload your server executable onto the servers of these services. And have your clients connect to the ip address of those servers. For example amazon has build in matchmaking and server scaling etc. Amazon has a server plugin for unreal you can read about gamelift here: What is Amazon GameLift
To build a dedicated server executable you need a source build from github.
It's also possible to use listen servers (a player act as the game host) but it's only recommended for local multiplayer, so the latency isn't high and only with just a few players.
But as mentioned it's the same as for pc, you can use for example use these tuts:
Dedicated Server related:
Unreals GameFramework related:
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