@ibalgin_ @Teressy_21 Hi !
I've taken note of your reports, and I'm sorry to hear that authentication errors are preventing you from enjoying the game !
Your messages have been moved to the Player Support section of the forum, to bring them the best possible visibility.
The error means that the wrong Ubisoft Account is used when launching the game via Steam.
If the problem persists after following the steps in our dedicated guide, I invite you to reach out to us via our Help website, where a specialist will check with you what can be done.
Don't hesitate to let us know if you have questions, or for any other Issue !