We have an HDX6000HD and I'm trying to dial in via the RealPresence mobile app using 4G. It's making a connection but with audio only, no video. The camera on the screen is greyed out. I'm getting a message "Participating in a video call requires sending and receiving large amounts of data. Be sure your service plan allows sufficient data transfer." I've checked on my iPhone setting and Mobile Data is switched on and I have 8GB available. Is there anything else I can try?