Mirroring on Kenwood head unit won't work

Slightly unusual Bingo location, but does anyone know anything about screen mirroring and how to make it work?
I've just installed a Kenwood DMX 125DAB in the Eos, which works fine, but I really want to be able to mirror the screen of my phone so I can use it for Google maps.
I have the Kenwood mirroring app, but can't seem to get it to connect.

Do I need to fiddle with the settings?

Help!

Sorted! I had to earth the "brake switch" wire from the HU to fool it that I wasn't watching YouTube while driving (all I actually wanted was to mirror Google Maps. A lot more useful if it works when you are moving).