Is this Office Professional Plus 2021 volume licensed version?
- Please open one Office app, such as Word > Account > Product Information, check whether there is "Update Option". If not, then it is volume licensed version. If yes, it is retail version.
- For volume licensed one, you need to use KMS activation, MAK activation.
- For retail one, Microsoft will give you one key, when you first time to use Office, you need to redeem this key that bound your Microsoft account with this key and activate Office.
Could you please show us, what error you got?
- You may take a screenshot and share it with us.
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