Settlement. The payment ends long after the receipt.

When a card is tapped, no money has moved. An authorisation is only a promise. Clearing works out who owes whom, and settlement is the moment the banks actually exchange funds, often the next working day. The two seconds you experience sit on top of a queue that runs overnight.

• Netting is the trick. Rather than settle every transaction, banks settle the difference between them, so millions of payments can close with a single transfer.
• The risk lives in the gap. If a bank fails between authorisation and settlement, somebody holds a promise instead of money. Much of payment regulation exists to shrink it.