First of all: This Mac Mojave 10.14.6 can't download from Applestore didn’t work. Neither did all the hints in the web like deleting the App Store’s cache or log off the Store and log in again, restart the Store or Mac.
After payment the download and installing procedure starts and then this message appears:
I just requested a refund via reportaproblem.apple.com and will buy the app through the website. I only chose the MAS because I prefer the automatic update-mechanism.
Glad it worked for you and, yes, it's definitely not happening for everyone. I'd say, it's a rare exception that downloading via the Mac App Store doesn't work.
Final update: A few days ago the download via MAS worked at last. Just a day later Apple accepted my refund-request, so MP3Tag is no more in the list of my recently purchased apps.
Well, I already bought the app via your website. I have the app, you earned some money, Apple earned nothing. Definitely a MAS-problem.