Pizza Express here in the UK has the best model IMHO. While ordering works as usual and you still have the option of paying the traditional way, you can also use their app. Select the restaurant, type in your table number and you’ll see what you had ordered and can pay for it. It even has options to split the bill.

No need to flag down a waiter, tell them you want to pay, yes, by card, and then watch him getting flagged down by 5 other guests until he makes it back to you with the card reader 10 minutes later.