This operation voids a payment for an order, when the order was created with a paymentType of auth.
For any auth orders, you will need to either capture or void the payment.
When you void the payment, you void for the amount of (up to) the original order value. You can make multiple voids and captures for each order, but the sum of captures (+ voids) must not be greater than the original amount charged to the customer.
The request supplies an optional amount field. If there is no amount supplied, the void is assumed to be for the full (outstanding) amount of the initial payment auth.