“This code has already been redeemed” Microsoft Error Message
This is what to do if you see a “This code has already been redeemed” error message on the Microsoft redemption page.
Check your services & subscriptions page

Sometimes the Microsoft redemption page glitches out during redemption and states the key has been redeemed, when it’s actually been applied to your account already.
Please check the services & subscriptions page of your Microsoft account to see if the key has already been applied and the software linked to your account on the following page: https://account.microsoft.com/services