The compass app in IOS has nothing to do with calibrating the compass in your drone.
When you attempt to calibrate the drone’s compass using Litchi, are you following the voice prompts about holding the drone parallel (then rotating) and then vertical with the nose pointed down (then rotating)? Does it give you a vocal warning that the calibration failed?
Are you doing the calibration at least six feet away from any metal? Are you wearing a watch on the arm used to hold the drone?
A compass calibration is rarely, if ever needed.