I totally get with the prepaid oyster that when it’s topped up I’m physically touching it to the contact so the data is transferred, but with a debit card (especially if I’ve say paid for something online) how does it know what’s on the card ?)
In: Technology
It doesn’t. But there are servers that do. And you talk to them and get “yes, Mr Smith can afford two pounds” back.
You can also do this slightly delayed to speed people up through the queue, as losing two pounds isn’t a very big problem, so you just verify that the card is an actual card and let people through, then debit the account a couple of seconds later.
It’s the same as the oyster card, you just talk to the credit card company instead of the oyster server.
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