By "official Apple website" do you mean you purchased this AirTag directly from Apple? The message you are seeing would indicate that this AirTag is no longer associated with your Apple ID.
If you did purchase this new, directly from Apple, and did NOT remove it from Find My from the iPhone you initially paired it with, it may be possible that it is defective.
As such, I suggest you contact Apple Support for further assistance with this matter. To do so, simply select the "Support" link on the lower left-hand side of this forum's web page.