Payd app signature screen freezes since last iPhone update

I am using the Payd app on my iPhone to process sales. Since a few weeks the signature screen zooms too large and then freezes, sometimes inadvertently finishing the sale, sometimes not. I believe the problem might have started after the last iPhone update. Payd does not seem to be aware of this problem and offers no solutions. The app is still available on the App Store. I have tried shutting down the phone, reloading the app from the App Store. My husband has the same problem on his iPhone 11. Any ideas?