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
From the little experience I have with it it _doesn’t_ know. It will try to block 1 pound once a day and after that it will not try to do any more transactions, only adjusting that one pound to the actual amount next day. If at that point you don’t have enough money you might go into negative on your bank account. Same if you tip in an American restaurant I guess.
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