I think a neat user experience would be to just get an NFC card printer, print them an NFC card that has a link baked into the card which would direct them to a webpage with their status, you could in theory do this inside glide if security is not an issue. OR you could build your own web portal. they can then just tap the card against there phone whenever they want to check the status, and then hand in the card in exchange for the keys when they get their car!
maybe you can crafty here: How to pass parameter to glide apps? - #5 by Darren_Murphy