What should i do in BP or program to create a session on the dedicated server like the sessions in Fortnite or any other Battle Royale Game?

My Plan is, that i create a Session when it is needed so the Players can join this Session, like in the Battle Royale Games.
I would like to create a Session on the Server, but the Server should be the host, not the Player.

As Online Subsystem i would use the Online Subsystem Python from this Link:
GitHub - RyroNZ/UE4MasterServer: This is a plugin for Unreal Engine 4 that adds server registration, deregistration etc with a master server..

I could also use this Online Subsystem: Making a Session System over Internet - Modding OSSNull c++ so it can be used over Internet, but this Subsystem doesn´t work with UE4.24.

But i am also open to use any other Online Subsystemm, which is not addicted to any Third Party.
If i have to program something in C++, that would be no problem, any hint or some Code would help me very much.

I tried to create a Session on the Server and when i didn´t opened a level afterwards, i got an Error on the Client:

Warning: SetActiveLevelCollection attempted to use an out of date NetDriver: GameNetDriver

And when i opened a Level afterwards the Game quits and the Error on the Client was:

Late PlayInEditor Detection: Level ‘/Game/Maps/Main_Menu.Main_Menu:PersistentLevel’ has LevelScriptBlueprint ‘/Game/Maps/Main_Menu.Main_Menu:PersistentLevel.Main_Menu’ with GeneratedClass ‘/Game/Maps/Main_Menu.Main_Menu_C’ with ClassGeneratedBy ‘/Game/Maps/Main_Menu.Main_Menu:PersistentLevel.Main_Menu’

Warning: OSS: Player ###### is not part of session (GameSession)

So i think i created a Session on the Server but also overrode the persistent GameSession, but thats not what i wanted. I wanted, that i create a new Session on the Server.

Can you please tell me what i need to do, that this will work?

Does anyone know what i could do?

Thanks in advance for any advice

For now I created a custom Battle Royale System.