(Possibly UK only) how does the contactless tap in on the London underground know when my debit card has insufficient funds?

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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 ?)

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6 Answers

Anonymous 0 Comments

It asks the bank. It has internet, it has your card details, it can just ask for X amount to be temporarily locked and see if the result is success.

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