Try on the iphone, go to settings and your need to find car play, click on this then use usb lead without bluetooth to connect, the display comes up on the head unit and you should see the mg app showing which means everything works.
Just check and cancel if its left a bluetooth setting.
Managed to get it to work - not sure what did it. Updated iPhone to the latest software, tried more cables etc. If anyone else has trouble I would suggest making sure you have the latest iOS running on your iPhone, make sure you are using an official Apple cable, use the usb socket closest to the driver (not the one with the phone symbol), have the phone unlocked before it is plugged in.