When a pre-authorization exists for a credit card payment, you "capture" the pre-authorization to complete the sale.
When you capture (process payment for) a pre-authorized credit card payment, the amount captured can be different than the amount that was pre-authorized. For example, if a customer at a restaurant adds a tip, the amount captured will be greater than the amount that was pre-authorized.
You can capture a pre-authorization only once. After the capture, the pre-authorization is always released in full, regardless of whether the amount captured is equal to or less than the amount that was pre-authorized.
For more information, see Capturing a Pre-authorized Credit Card Payment.