How to trigger Camera access popup by script?

When accessing the iPhone Camera, a popup appears to ask the user for permission.
In order to create a good UX flow, I want to ask for permission before I throw the user straight into my AR Scene.
How can I trigger the permissions popup by script?

Application.RequestUserAuthorization(UserAuthorization.WebCam) does not work.
("webcam not found" is what you get)

Hmm, the example script does work: https://docs.unity3d.com/ScriptReference/Application.RequestUserAuthorization.html