How to display AR model_viewer plus on Android

Question

Hello when I run my code and press the cube to see the 3 objects in AR the camera don't open it just show me the object in Black page with a full 3 d object

   child: Hero(
              tag: widget.product.id.toString(),
              child: ModelViewer(
                src: 'https://modelviewer.dev/shared-assets/models/Astronaut.glb',
                ar: true,
                arPlacement: ArPlacement.floor,
                cameraControls: true,
                autoRotate: true,
              )

I want to see the object with augmented reality