[2022] Purchased game on Steam a while ago, can't play it now.

Hi there @VikingBloodGod thanks for reaching out. I am sorry to hear about this error showing for both you and @KoolGuy!

An authentication error usually happens if the Ubisoft account that is logged into the Ubisoft launcher is not the same as the original Ubisoft account that was used to first activate your game. You can resolve the error by logging back into that original account; however, I can understand that can be tricky if you do not recall which account was used. While your Steam profile can be associated with any account; only one Ubisoft account can be used to access your game. If you remember using a different email address closer to when you purchased your game I can suggest to try logging back in using older credentials to help pinpoint the correct account.