The QR code cannot be scanned properly. – KORG app Help Center

Check if the number of the QR code that you are trying to scan is correct. The number of the scanned code will appear on the bottom of the iOS screen, so if the code is shown to have been scanned, proceed to the next QR code.
Adjust the position of your iPhone/iPad to scan the QR code from the front with no distortion.
Reposition your Nintendo Switch to avoid reflections on the screen. Reflections on the screen can affect QR code scanning.
Change the size of the QR codes by pressing the X button in the QR code screen of KORG Gadget for Nintendo Switch. Use “Magnify” to scan them easier.
“Magnify”: Magnify the QR code so that your iPhone/iPad can scan it better. (However, it will increase the number of the QR codes.)
“Shrink”: Display a QR code densely packed with more data. As it will make the code more intricate, it will be more difficult to scan it with your iPhone/iPad.