Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
This looks like a local licensing cache issue on the iMac, especially since the same Microsoft 365 subscription works on the MacBook. The activation notice may be related, but I could not verify that the current service issue specifically causes this purchase-association error.
Here are some suggestions you can try:
Confirm the subscription is still shown as active under System Settings > Apple Account > Media & Purchases > Subscriptions. Also make sure the App Store is signed in with the same Apple ID used for the original purchase.
Quit all Office apps, then use the official Office license removal tool. Deleting Keychain entries manually may not remove all local licensing files. Restart the Mac afterward.
Remove Word, reinstall it from the Mac App Store, open it, sign in with the Microsoft account already used on the working MacBook, and select Restore previous purchase. If the subscription was originally purchased through a different Office app, restore it from that same app.
If the same message remains, contact Microsoft Support and provide the Apple purchase receipt. They will need to check the account association on the licensing side.
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Thank you for your patience in reading, I hope this information has been helpful to you.
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