I switched the camera on and off using the following under the regular (not cloud) targets:
GameObject cam = GameObject.Find("ARCamera");
cam.SetActive (false); //to switch off
cam.SetActive (true); //to switch on
I need to keep the camera off for a period of time when my system work in something not related to camera scanning.
However, when I moved to cloud I lost this feature. This means the Camera has to stay on from the beginning to the end.