in the customers hand and still in their bank account. That was one scenario. And known examples involved two separate computers that had to communicate, and one had some glitch power maybe, over heating, it happens. But the system allowed the transaction to be sent to head office, but not to the other computer. That is definitely bad programming.

In the early days of computing they had a system of keystroke logging as a back-up. Modern terminals and systems are far too complicated for that.

I saw a case yesterday in the Folk Museum at a Folk Day. The till had a 7 inch monitor thingy with a touch card logo/area. People presented their contactless card and most (me too) went all over the surface to find the C-spot. Then up comes the receipt options, I was about to go for "print" when they entered another transaction and my options disappeared. No way to get the paperwork!
The thing offered e-mail receipt - apart from the time it would take, do I give it away to every trivial vendor?