Session join fails

Hi.

I’ve managed to create EOS sessions, the portal shows them.
I used Session interface → CreateSession, and JoinSession on the client. Both of the callbacks return success, but when I’d RegisterPlayer the player, it gives me a EOS_InvalidParamters result.
I found out, that

EOSIds.Add(EOSSubsystem->UserManager->GetProductUserId(*PlayerId));

Fails. Not fails, but doesn’t return right, and EOS can’t register players because of it.
If I replace EOSIds.Add with EOSIds.Add(“Test”); it registers a “player” on the portal named Test, but I think it should contain Unique IDs instead of fixed strings.

The client enters the server world, and spawns, i can see other clients but the dev portal bothers me.