open device camera with vuforia

hi, I am bigginer to unity and vuforia, I try to open device camera with vuforia ARcamera but I can not. every sample code which I have tried it just show black screen on real device , I read for opening device camera we should disable webcam in vuforia configuration but it always shows black screen. would anybody help me?? I get mad:(:(:(… please help
by webcam every thing is ok, problem is with real device

For ios devices you need to allow permission to access the camera,
to do this in unity go to:

-build and settings
-player settings
-inspector
-camera usage description
then write there this: “target recognition”
and thats it, when you run the app again it will ask you to access your camera device and hopefully this will solve your problem