iPhone 14 Pro/Max seems to have a known camera issue which we hope Apple will fix soon in a software update.
The issue is that third party apps (ie - apps that were not made by Apple) are unable to access the correct camera on the back of the phone and therefore in the case of Haystack, it makes it impossible to scan paper cards using the app's 'scan' feature.
While we're confident Apple will fix this issue, in the meantime, here is how to overcome this issue:
Take a clear photo of the paper card you want to scan using your iPhone's normal camera app
Open the Haystack app and tap the 'scan' option at the bottom of the screen
Tap the 'gallery' icon (represented by two stacked rectangles icon) and choose the photo you took in step 1 from the gallery