If you're a Screens 4 user with a Screens 5 offer code encountering a "Cannot redeem code" error, here are steps to resolve the issue:
App Store Issue
It seems there are challenges with redeeming offer codes on the Mac App Store app. Try activating the offer through the iOS App Store if initially attempted on the Mac App Store, or vice versa.
The problem could also stem from an issue with the payment method associated with your App Store account. Thoroughly review your App Store account for any payment-related issues. If the problem persists, reaching out to Apple support may be necessary.
Also, please note that the offer code is applicable exclusively to an annual subscription and cannot be utilized for a Lifetime subscription.
AdGuard
Certain users have noted that AdGuard might impede access to the App Store, hindering Screens from connecting to the Apple server for your purchase. If you have AdGuard or a similar tool installed on your iOS device or Mac, kindly review its settings to ensure unobstructed access to the App Store.