When you pay at places like restaurants, bars, hotels, salons, or taxis, the merchant may temporarily hold up to 20% more than your bill to cover a possible tip.
As long as your balance covers the bill plus this extra amount, the payment is approved.
If you do not leave a tip, the unused amount is released back to your card.
If your balance is low, the merchant's system may automatically know how much is available on your card and perform a partial payment. If not, tell the server or cashier exactly how much to charge to your card, and pay the rest with another form of payment.