Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hi Paul,
Maybe it's not the product key but product id, seethis thread.
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To find your product key, see:Find your product key for Office for Mac 2011
Meanwhile,support for Office for Mac 2011 has ended. Continued mainstream supportrequires upgrades to Office 2016 for Mac applications as part of Office 365 ProPlus orOffice 2016 for Mac. We suggest you use Office 365 plans to get the latest Office applications which will give you a better user experience.
Thanks,
Jim