Dedicated Server Session in Steam not findable

So I compiled my project from an unreal source build into a dedicated server. The Project is using the Steam OnlineSubsystem.

The Server seems to start correctly

This is the RegisterServer function overridden by me to register the session in the online subsystem

So then i have a client with a UMG button calling a c++ function that inside of my game instance fires following “FindSessesion”:
(It’s being called from an own c++ UBlueprintFunctionLibrary that provides a “FindDedicatedServerSession” BlueprintCallable, see 4th picture)

But no matter what I do I can’t get my Client to find the dedicated server’s session. how can I figure out why it’s not being found? What could go wrong here? Hopefully, someone can help me here, i sooo need to get this to work and I’ve been working on this for some time now. I have already reached out to Discord and Reddit but got nowhere so far.

Looking forward to your responses, thanks, guys.