[ErrantX]

Your card doesn't know the balance, it doesn't work like that.

Offline transactions mostly died off when the limit in the UK for contactless was raised to £100. At £20/30 (the original limits) issuers/merchants risk accept some payments not being valid (and the total limit before you had to chip and pin was fairly low top).

And worth saying, the merchant has some control on the terminal but mostly the decision of offline/online is down to the issuer and configured on the card.

[mijoharas]

Out of interest is this both debit and credit cards, or just debit?

[daveoc64]

Some debit cards don't allow offline transactions, usually when the cardholder isn't allowed to be in debt.

In the olden days, you'd get a Visa Electron or Solo debit card in the UK if you were under 18 or had a poor credit history.

Visa Electron and Solo were online authorisation-only card brands (also known as "immediate authorisation").

If you didn't have enough money in your account, the transaction would be declined. Visa Electron cards didn't have embossed numbers on the front, so couldn't be used with the old-fashioned card imprinters.

Visa Electron and Solo have been discontinued now, so people with poor credit can get a Visa Debit or MasterCard debit card, but with offline authorisation disabled.

That does mean those cards can't work in some places (e.g. on aeroplanes or trains).

Credit Cards generally always support offline authorisation.

[ErrantX]

Mostly identical. Credit cards will probably have different risk rules though - after all it's their money not yours :)