Hello, I’m Quinn and here to help!
The “TooManyRequests” error means Microsoft temporarily blocked the product key redemption because there were too many attempts in a short time. It’s a security limit, not necessarily a bad key.
Please wait at least 24 hours before trying again, and avoid multiple retries. When you try again, try using a different browser or private/incognito mode.
If it still fails after 24 hours, the key may not have been properly activated at the store or could be invalid. May I ask where you purchased the Office key? If it was from a retailer, you may need to contact them. If it was bought directly from Microsoft, you’ll need to contact Microsoft Support with your receipt and the error details.