Scenekit spotlight with Gobo effect

I saw it's possible that you can use a gobo as light effect like in the real world, flag some lights off.
Can someone help me to get the gobo effect to work?

In the following example you will see a cube with a plane below it and a spotlight above it. I would like to load a pattern (image) in front off the spotlight-source which would flag (block) certain parts of the light.
Expected behaviour would be that you will see part of the pattern on the top of the cube as you will see part of the blocked light pattern on the plane.

Could anyone help me with solving this gobo puzzle?

Code Block 
  view.backgroundColor = .blue
	let sceneView = SCNView(frame: self.view.frame)
    self.view.addSubview(sceneView)
    view.bringSubviewToFront(sceneView)
    sceneView.backgroundColor = .clear
    sceneView.allowsCameraControl = true
    let scene = SCNScene()
    sceneView.scene = scene
    // Add camera node
    let camera = SCNCamera()
    let cameraNode = SCNNode()
    cameraNode.camera = camera
    cameraNode.position = SCNVector3(x: 0, y: 0, z: 0)
    scene.rootNode.addChildNode(cameraNode)
    // Add a cube to the scene
    let cubeGeometry = SCNBox(width: 0.5, height: 0.5, length: 0.5, chamferRadius: 0.0)
    let cubeNode = SCNNode(geometry: cubeGeometry)
    cubeNode.position = SCNVector3(x: 0.0, y: -0.5, z: -1.5)
      // Make the cube white
    let whiteMaterial = SCNMaterial()
    whiteMaterial.diffuse.contents = UIColor.white
    cubeGeometry.materials = [whiteMaterial]
    scene.rootNode.addChildNode(cubeNode)
    // Add a plane to the scene so we can see the lights & shadows
    let planeGeometry = SCNPlane(width: 100.0, height: 100.0)
    let lightGrayMaterial = SCNMaterial()
    lightGrayMaterial.diffuse.contents = UIColor.lightGray
    planeGeometry.materials = [lightGrayMaterial]
    let planeNode = SCNNode(geometry: planeGeometry)
    planeNode.eulerAngles = SCNVector3(x: GLKMathDegreesToRadians(-90), y: 0, z: 0)
    planeNode.position = SCNVector3(x: 0, y: -15, z: 0)
    scene.rootNode.addChildNode(planeNode)
     
    // Create a spotlight
    let light = SCNLight()
    light.type = SCNLight.LightType.spot
    light.castsShadow = true
    // Create a Gobo mask:
//    if let gobo = light.gobo
//    {
//      gobo.contents = UIImage(named: "gobo")
//      gobo.intensity = 0.5
//      //light.categoryBitMask = -1
//    }
     
    // Create al lightNode
    let lightNode = SCNNode()
    lightNode.light = light
    lightNode.position = SCNVector3(x: 0, y: 10, z: -1.5)
    let lightAngle = -90 * Float.pi / 180 // light facing down
    lightNode.eulerAngles = SCNVector3(x: lightAngle, y: 0, z: 0)
    scene.rootNode.addChildNode(lightNode)