Hi, I'm John! I will help you with this.
Since you started the Microsoft 365 trial through the App Store, your Mac might still be tied to an older sign-in or cached license.
To fix this, you’ll want to fully remove the Office apps and any leftover license files, then reinstall them cleanly. Here’s what you can try: https://support.microsoft.com/office/uninstall-office-for-mac-eefa1199-5b58-43af-8a3d-b73dc1a8cae3
Then reinstall Office from the Mac App Store, then sign in using the same Apple ID you used to activate the trial.
This usually forces the apps to pick up the correct subscription from your Apple account.
I really hope this information is helpful! Let me know if you have any further questions or concerns.
Regards,
John J.D.