I'm also having the same issue. I purchased the last version, but restore purchase doesn't work on the macOS store version.
By the way, setting up the cloud sync was a bit annoying and the UX was not great because I had to switch to the app store version. After downloading and installing the app store version, it treats it like a fresh install and I had to setup the cloud sync by logging into Dropbox... which is obviously difficult, since the password is stored in Enpass!