The Lidl branch I most use is at Clapham Junction. They have number recognition cameras, and ask you for your car number at the checkout. Which then gives you up to 90 minutes free parking.
Had a demand for a fine from the company that runs it for them. On that occasion, the till person obviously forgot to ask me for my details. Not that I noticed at the time. And they could have changed the system anyway.
Emailed the car park company and said I'd paid by plastic so they could check with the store easily that I'd used the store on the date and time in question.
Some time later, I've had an email asking me to prove I made a purchase. They want a copy of the till receipt.
As it happens I do still have it - as I bought something with a warranty. But had it been just groceries, would have been junked the same day.
So I've told them to check themselves. Be interesting to see what happens next.