Unlicensed product message on office program

My Office product is suddenly showing unlicensed product message on the top of the screen. I have a valid license and it was working fine for many years. Not sure what changes I would have done to get this unlicensed product issue.

I will explain, the office product comes with a subscription license for 365 product or any other volume editions. This product expires after the subscription is over or if you have not renewed on time.