Calibrator Requires Camera Access
You can't get past the message: Calibrator Requires Camera Access. In order to calibrate your sensor you need to allow Structure Sensor Calibrator to access your camera.
On your iPad/iPhone simply go to:
In the left pane, scroll down until you find Calibrator:
Tap Calibrator. In the right pane, you will see all of the permissions Calibrator needs. Toggle the Camera permission to "On".