How do you create a session configuration using ARKitWorldTrackingSessionConfiguration

Hi guys does anyone know how to change the current ar session, I'm trying to have it so the plane detection for horizontal planes is turned off, I call this function using a event inside the ARKitManager script to stop the plane extending, however it doesn't work


public void disablePlaneExtention()
{
m_session.Pause ();

// create new config
ARKitWorldTrackingSessionConfiguration config = new ARKitWorldTrackingSessionConfiguration();

// set plane detection to none
planeDetection = UnityARPlaneDetection.None;

config.planeDetection = planeDetection;
config.alignment = startAlignment;
config.getPointCloudData = getPointCloud;
config.enableLightEstimation = enableLightEstimation;

// run session with new config and doesn't work
m_session.RunWithConfig(config);
print ("detection turned off");
}