I saw the response in the FAQ:
"The Remote Desktop feature is not working.
You may need to allow popups for the remote access to work."
I'm using Cayenne on a tablet, and I'm getting the message, something to the effect of "tell the remote user to press Share This Computer". However, I don't see anything on my Raspberry Pi desktop that would indicate the it's being accessed remotely. Nothing changes on the desktop.
When you say "allow popups" are you talking about settings in Chromium? My web browser for my RPi. I don't think the GUI has a setting like this.