Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Carole,
The key code is not the license itself. The key code is to be redeemed, upon first time using, so that it can be associated with the Microsoft account, then moving forward, that subscription is tied to that Microsoft account. In your case, the plan owner would be the company owner, if he has already redeemed it. So it makes sense that it says it is already used.
In order for you to share this family plan owned by the company owner, tell him to use this instruction to invite your Microsoft account instead. https://support.microsoft.com/en-us/accounts-billing/subscriptions/share-your-microsoft-365-subscription Once that part is done, you just need to sign into your Microsoft account in the apps to use them.
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Now, if the company owner received the key code but has never redeemed it at all, and you got the error first time trying to redeem it, then you need to contact AAFES. They are the reseller here. It was purchased directly from Microsoft, so contact Microsoft support will not help in this case because billing and payment were handled by AAFES.