If you are a Screens 4 user and have encountered a "Cannot redeem code" error while trying to use a Screens 5 offer code on your Mac, please follow these steps to resolve the issue:
Mac App Store Limitation
Currently, the Mac App Store is unable to process offer codes. However, you can redeem the offer code through the App Store on your iPhone, iPad, or Vision Pro.
After the offer code is successfully redeemed and applied on one of these devices, the benefits will also extend to your use on your Mac.
We anticipate that Apple will address this issue in a forthcoming macOS update.
Please be aware that this offer code is valid only for an annual subscription and cannot be applied to Lifetime or Monthly subscriptions.