mapbox_gl white screen

I need to use map-box i am sure that all the configurations are fine. but when i run the app the output of the map is like this:

The Map Widget is:

MapboxMap(
          accessToken: MAP_BOX_ACCESS_TOKEN,
          initialCameraPosition: CameraPosition(
            target: LatLng(34.123456789, 34.123456789),
          ),
          onMapCreated: (_) {},
          onStyleLoadedCallback: () {},
          styleString: MAP_BOX_URL,
        ),

I am using the library: mapbox_gl