The slim metal disc can be stuck to the rear of the phone or slid into the case between the phone and the case. The magnet is part of the mount and is very strong. I've been using my iPhone X with this mount for over a year and it's never come loose.
Another airport hotel horror story - this time it’s an A6.
It seems to me that they’ve met their obligations by contacting you through two separate channels - text and email. The emails reached you, but if you don’t check the content of your spam folder regularly that’s hardly Admiral’s fault.