How do I record video on iOS with external audio interface?
On your iOS device, launch Camera App. Select the desired recording setting (eg. Video).

THEN plug in your external Audio Interface. Your camera connection kit should already be plugged in, but you should only plug the audio interface usb lead into it once the camera app is running.

Record. It will take in whatever is on channels 1 and 2 and record with your video stream.

NOTE: If you either close the Camera App, power down the iOS device, iOS device goes to sleep or you disconnect your interface - you will need to repeat the above procedure to capture again.

Other issue, these is NO INDICATION you are recording audio from the external interface - so you may want to test the procedure a few times to make sure you know it works for you so you can reproduce exactly in a real situation.