I don't know if I can make a suggestion that might be seen with all the activity here - but if it were me designing it, I would have an option to lock-in a sing

I don't know if I can make a suggestion that might be seen with all the activity here - but if it were me designing it, I would have an option to lock-in a single card via the smartphone app. Or, maybe only allow switching within a foot or two of your smartphone. That would eliminate the concern people have about where the waiter accidentally pushes the button and switches the active card.