It’s not like you can (could?) keep a block „just in case” and thus many shopkeepers wouldn’t even bother in case of outages.
Depending where you live a good old trust can be a currency. Humans are great when it comes to adaptation, I bet I could just write on paper name, CC number and leave it on a paper for shopkeeper and everything would resolve just fine..
Most retail workers are GenZ and struggle to understand what this would even look like because they’ve never conducted any transaction without POS computers (for looking up prices, for tallying them, for figuring tax and total, and computing change), so even if a dusty manual in the stockroom technically spells out a method of ringing sales using nothing but pen and paper and maybe a solar calculator, I would be surprised if any of the clerks working any given day would have the initiative to initiate an offline protocol. Most likely the store manager would usher customers out, lock up the store, keep the staff for 30 minutes to see if it came back on, and then go home.
I've only seen a few but I believe they have springs on the inside and roll on little wheels similar to how desk draws roll. Most can be opened with a key to trigger that event.
(And in many cases you cannot legally pay large amounts of money in cash, it has to be electronic)
So it is perfectly legal to use pen and paper and a cash box.
https://www.lexware.de/wissen/buchhaltung-finanzen/neue-rege... https://www.lexware.de/wissen/buchhaltung-finanzen/kassenbon...
Many other EU countries have similar regulations, and in some cases had them for a long time.
Receipts or invoices are the basis for a firm's whole economic activity, including the underpinning of their financial reporting, their tax burdens etc. And businesses failing to provide receipts erodes not only the tax base, but also any rights a consumer may have.