As i already explained. That is not the SteamID. The UniqueID is platform dependent, the PlayerID is only valid while the client connected to the server (Session ID?).
If you want to store information about your users, you need the steam id. (Credits / User Points / Stats / Ranking and so on…)
Kheka i would make a new UCLASS with static methods exposed to the blueprint api that returns the SteamID as an FString.