Can't be the usual contact-less payment system, has to be targetted at eligible types of retailers is the whole point if I understand correctly.
The majority of retailers do accept contactless payments though.
And then you will only want to do part-spends in many places, so needs to be a payment system with its own infrastructure which would be very very expensive to set up, I should think if it worked "at moment of paying" like contactless does now.
It would literally be taking money from a balance? No huge infrastructure needed. It would work in the same vein as any other transaction.
Besides, contactless is only £30 limit, so probably just mean digital or card payments
It's actually £45 now. However when you use your phone the limit is quite often set much higher than that