You may need an activation code if:
To request an activation code, you must first get a request code. To get one, see Find request code for manual activation (US Site).
Once you have that, activate your licence at Autodesk Product Registration and Activation.
Important: Autodesk no longer supports manual offline authentication for 2021 products and later. If you have a perpetual licence for a 2021 product or later and want to use it offline, activate your software by going online one time to register. You can then use the software offline. This change doesn't apply to subscription network licences or previous versions that you already activated offline. You can continue to use them as before.