Even though I said the app worked for me, the application was yesterday really removed from the app store.
Now it is indeed back in the app store, but it still does not work on the ipad 4 with a fairly recent ios. And well, “What a difficult world it is for a small programmer”, but it is also a € 33 app and it is expected to work well … Again, on my ipad pro 2020 works fine, but I understand very well the irritations of the other people where the app is not working.