That’s an interesting solution, yeah. Perhaps, in that situation (when authorisation from the app doesn’t arrive in time), it could block contactless payments and require you to enter the PIN instead?
That’d still be some manner of two factor authentication I guess?
This has been suggested before and Monzo said the speed card transactions are processed means a transaction would fail due to time out due to waiting for a cardholder response
Yes, you don’t have time in the however many milliseconds are allowed to do a back-and-forth communication to the phone with customer interaction in the middle. Useability is probably questionable too since you’d now need the phone out and ready every time you try and pay for something so making a payment is suddenly a 2 handed operation.
In the future, contactless might be on/off toggle (ATM and online payments as well, all three separately). This kinda means that if you disabled contactless method, you’d be always forced to pay with PIN. Could that be a viable solution for your idea? I think that inserting a card and validating with a PIN should be operationally faster (for human) than waving contactless, unlocking a phone, opening an app, validating in the app and waiting for the terminal to accept the payment.