Thought I would post this as this issue has been driving me nuts over the last couple of days.
Had Office 365 installed via a HUP product key and used it for about a month when I got a banner message when opening up an office application that my license status could not be verified, and to please sign in. When I checked the license it showed as valid and the product reported that it was activated. Signing in produced a message that there was no product associated with my Microsoft account so I simply re-entered the product key by choosing to activate without signing in. That was always successful and made the banner go away until I reopened the product.
Long story short...after scrubbing Office from my PC, reinstalling, scrubbing and purchasing a new HUP key, scrubbing and purchasing a retail Office 365 subscription, checking ports, disabling firewalls, and then finally factory resetting my PC reinstalling using only the Office 365 subscription...I still had the issue.
Last thing I tried was to use the Office licensing scripts to evaluate the product keys (should have been the first thing I did). Open a command prompt, go to (different for 64 bit) C:\Program Files (x86)\Microsoft Office\Office16, and type: cscript ospp.vbs /dstatus
There were apparently 3 product keys installed: two that had 30 days or so of validation and 1 that stated it was "licensed". I used cscript ospp.vbs /unpkey:<Last five characters of product key> to get rid of the temporary keys and left the last one. Problem fixed.
How in the world can a brand new install of Windows 10 and Office 365 install directly from a valid Microsoft account showing a valid subscription with zero PC activated yet produce this problem? I didn't find any other posts so maybe I'm unique.
Now I need to go back and restore my files. Oh, and yes I did attempt to contact an actual person. After I got through the chat help bot that verified my product keys were good and gave me a download link for a FixIt file (didn't work), I decided to contact a person. Call back queue was 257 minutes...still waiting.