Your license - either Mac App Store or website - is only valid for the version you've purchased (see Installation Guide).
Did you recently upgrade to macOS 10.15 Catalina and your license is no longer working? Please use this troubleshooting guide instead.
If your license suddenly stopped working, the most common cause of this is that your Web version was updated by the Mac App Store. This can happen if you've previously downloaded the app from the App Store, since Apple automatically replaces non-App Store versions with App Store versions.
To correct this issue, you'll need to delete the Mac App Store version and re-download the Web version (see your order receipt for the link). We have raised multiple tickets with Apple regarding this "feature" of replacing non-App Store versions with App Store versions, but they have yet to make changes on their side.
To stop this from happening again in the future, you must hide your Mac App Store purchase. It will be in your list of Purchased items. (On macOS 10.14, just click on your name in the lower left to see your purchases).
For more details on restoring your license, see: