AR in webXR, layers and stencils

Hi, when using webxr in AR,

I have found that I cannot turn layers on and off by setting my camera to different layers
I know that the first 3 layers are taken and have assigned object to the next three layers using
children[4].layers.set(4)

and then

camera.layers.enable(4)
camera.layers.set(4)

this does not make the object appear. May I ask if there is a special procedure that I need to perform?