Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hello,
Use another web browser or device and open an Incognito tab.(Private browsing session)
Go to this link here to redeem the product key.
https://setup.office.com/redeem/enter-key
Click 'Get Started' and enter the 25-character product key you have for the Office 365 Personal Subscription.
Sign in with your Microsoft account to redeem the Office product successfully.
If you are still having issues, connect your device to another Wi-Fi network, such as a mobile hotspot network, and redeem the Product key.
If you are using the same web browser, clear your browsing history, cache, and cookies.
Once redeemed, the product appears in your Microsoft account here -