What should i do 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.

Does anyone know what i could do?

Thanks in advance for any advice

Unreal Engine offers support for a few Online Subsystems already. If you open the editor and go to plugins you can activate support for these.

The barebones online subsystem of Unreal is called “Null”, you could start from there and work your way up if you want something specific for your needs.

Thanks for your Answer.
But i don`t know what i need to create a Session, so it is like a Session in a Battle Royale Game.
So when no Session exists, a Session would be created and the Host should be the Server.

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Warning: SetActiveLevelCollection attempted to use an out of date NetDriver: GameNetDriver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

I appreciate your help with this.