Hi, tito mascarenhas
For a personal copy of Office 2024, you redeem the key online first, then activate Office on your Mac by signing in with the same Microsoft account. You don’t enter the key directly into Word.
Here are some suggestions you can try:
Open Office setup, sign in with your Microsoft account, and enter your 25-character product key. If it says the key has already been used, skip redemption and use the account that originally redeemed it.
Download Office using that account, open Finder > Downloads, and double-click the Microsoft Office installer.pkg file. Follow the installation prompts, then open Word and select Get Started > Sign in to activate.
If you installed Word or Excel from the Mac App Store, remove those apps and install them directly from Microsoft instead. App Store versions don’t support one-time Office licenses.
If it still fails, please share the exact error message, your macOS version, and the Office edition you purchased. Please don’t post your product key.