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.
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.