Hi Nefusadi,
There are a couple things you can look at, first of all, make sure “OnlineSubsystemGooglePlay” is one of the uncommented dependencies the Build.cs.
Also, check for DefaultPlatformService in your DefaultEngine.ini file. On Android, this should default to “GooglePlay”, but it might be getting overridden. You can try making sure this is in your DefaultEngine.ini:
[OnlineSubsystem]
DefaultPlatformService=GooglePlay