I also have issues with the UPC ID Checker application. Tried multiple time to check my ID using my passport and it always failed at the 2nd page. After multiple failed attempts now it does not even recognize the QR code.
I have restarted my phone (a Samsung A52) multiple times, cleared app data multiple times, cleared app cache multiple times, re-installed the app multiple times and also tried the app from a different device (an iPhone).
What other option are available for identification beside paying 40chf (to be identified by the postman)?