PAVE Inspect requires that the Portrait Orientation Lock feature on your iPhone be turned off, such that when turning the device sideways, the screen changes to landscape mode. You will not be able to capture images if the phone is in portrait mode.
The Portrait Orientation Lock feature is on causing the screen to stay in portrait mode.
1) Swipe down from the top-right side of your iPhone screen to open the Control Center.
NOTE: If you have an iPhone with Touch ID instead of Face ID (iPhone 8 or prior), instead of swiping down from the top-right, swipe up from the bottom-center.
2) Click on the Portrait Orientation Lock icon so that it is no longer highlighted and it says "Portrait Orientation Lock: Off".