There are nuances. I've got it on my iPhone and on my iPad and something I have to make sure that I've got the phone waking up or even starting the Tesla app. Not always though, where sometimes it just works with the phone in my pocket. The auto-lock is far more consistent since it's just looking for an absence of the device. I'm also thinking that it doesn't necessarily unlock until someone goes to the door or trunk.
With a Tesla loaner there was a QR code that popped up periodically on the display for adding the car to the app. I found a photo someone posted of a Hertz rental. I believe it changes the QR code each time and it's just a URL that then brings up the app.