The Notification setting will uncheck itself if the server doesn't have any devices to send the notification to. The most common reason for that is if the iCam Pro app is in free mode, because the app doesn't connect to the server when it's in free mode.
Please make sure the subscription is active in iCam Pro > iCam Pro Store running on your iDevice. If it says Subscribe and you have already purchased the iCam Pro Service, please click Restore.
If the app is in paid mode, are you able to view the camera when the phone is connected to the cellular network (not the local Wi-Fi network)?