Obviously this is about the power outage in Spain.
While normally, if a card declines, people would probably have to leave their IDs with the restaurant while they went to get a withdrawl from their bank; this is a power outage, withdrawls wouldn’t work. It would be silly to arrest people because of a power outage. So I’m assuming people just have to give the restaurant owner/management their identity info with a promise to pay?
And power outages shouldn’t affect buses, since they run on gasoline/diesel, but the payment system processing transit passes might not work. Do buses still get run during a power outage and they just let people on for free, or do they just shut down the bus lines?
Card payment terminals use the network for card authorization, but depending on the merchant agreement with its card processor, authorization (at least back in my day) was typically only needed for charges above say $50. Otherwise the bank would pay up and eat the loss if something went wrong.
If you’re old enough to remember cards with raised numbers on them, those existed so the merchant could make an imprint of the card number on carbonless paper using a hand operated gizmo with rollers and carbonless forms. That used no electricity at all. You’d sign the piece of paper and the merchant would turn it in to the bank. That was simply how credit cards worked for quite a long time. Electronic terminals, and especially portable electronic terminals came along later.