Are you 100% certain you are trying to activate 4.0.2 from the plugins menu and not an older release from the Filter menu?
If so then lets do a screen share through Chrome Remote Desktop so I can look at it. It is a free add on for the Chrome Browser which will allow you to share your screen with me.
It doesn’t make any sense because all of the newer plugins use the exact same activation system.
Let me know after you have installed Chrome remote desktop. Then you can send me an email with an access code and I can look at it with you.