License keys that were generated for EventSentry prior to v2.50 will work with all versions of EventSentry, including version 2.80.
License keys for EventSentry v2.50 and later will only work with versions v2.50 and later, they will not work with version 2.43 or any other earlier versions.
You can contact our support department if you have purchased an up-to-date version EventSentry and need to get a license key for an older version of EventSentry, 2.43 or earlier.