"Phone is critically full" error message when recording video directly to iXpand

this is a limitation of iOS. Pictures can be taken directly to a storage device connected to the lightning port however due to iOS limitations video must first be captured to the iOS devices internal memory. Once the video is complete it will be transferred from the internal memory to the external storage device. Unfortunately due to this limitation you would need to free up some internal storage space to shoot video even using the iXpand in app camera.