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How are restaurant tips charged? The card is run, and then you add a tip, and at some point they enter in the tip amount I assume. Would that charge show as going through at the original time, or at the time they revised the total? I imagine if they come through as special revisions, allowing those up to a certain time after the original charge and up to a certain percentage over the original amount might be sufficient, as long as there's not multiple different ways that different vendors (restaurants) do it because they don't know what they are doing...

They obtain an "authorization" in some amount, probably the bill minus tip, then fulfill it later for the amount of the bill plus tip. This is a ubiquitous practice with payment cards - for example, when you pay for gas with one, the POS authorizes some small amount to ensure the account can accept debits before unlocking the pump, and later fulfills the authorization for the price of the fuel you purchased.

Authorizations of this sort count against your available balance, and time out eventually if not fulfilled; when you look at your account and see "pending charges", this is what they actually are. Not all charges use this process - when the total amount is immediately known, it's generally immediately charged as well. But in any case where the amount may change or the account requires validation before a transaction can proceed, this is how it's done.

Presumably, since a valid authorization constitutes an agreement to pay the charge (hence the language under the signature line on your bar tab), the "enable" step you perform via the API would permit the authorization to occur, and fulfillment would work the same way it does now.

> How are restaurant tips charged? The card is run, and then you add a tip

That sounds bizarre and backwards to me! I guess we live in different countries/regions with different conventions. So it probably depends on what people do in South Africa.

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