Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
The error activation message is when you use the apps, like Word, Excel, right?
If so, can you go to your microsoft account https://account.live.com > subscriptions, tell me the full name of the subscription, and make sure it is active.
Then I need to know, what operating system are you using? Windows 11, or macOS? If it is macOS, which version?