It totalizes the operation in progress, calculating all the benefits that can be applied for that customer, and for that checkout specifically.
The caller will be responsible for applying the specified discounts, both to the OrderLine and Order level. Wapping assumes that the benefits will be applied as informed.
The benefits are preauthorized, meaning that the customer won't have them to use in another checkout at the same time.
The preauthorization can be released after certain time has passed, another total operation is performed, or a cancel operation is called.
When the last step (Commit) is done, the informed benefits will be substracted from the customer's wallet.
All the calculations are done in the Wapping side, meaning that the POS or ecommerce only has to apply them as-is, without performing calculations or any kind of logic.

Important: The amounts informed cannot have the discounts from wapping, in the event of a re-totalization, make sure to inform only the amounts without wapping discounts, otherwise there might be a recurring discount.
Important: The amounts in the orderLine has to be specified with all the external discounts applied (discounts from other sources than wapping, if it applies). The discountAmount in the CheckoutSession level is to inform
about all the discounts (again, external to Wapping) that are applied to the order level, if any.