This requires that the business in question used their solution, that the customer has a compatible phone, AND that the customer has downloaded the app. A piece of paper doesn’t.
Another problem is, what do you do if someone has entered the queue but doesn’t actually show up? Do you wait?
Last time I was at a clinic, I booked an appointment by phone in advance, and when it was my turn, they called me up. No paper needed. No app needed.
This whole thing sounds to me like a solution in search of a problem.