Any authorization will have an amount and an 'Approval Code' linked to each authorization.
Search for a credit card that has this value, and then click 'Delete Card' in Manage Credit Cards to release the authorization, if the card holder and manager deem this necessary. See Manage Credit Cards and Incremental Authorizations
This frees up the spending ability for the card holder, with the amount of time dependent upon the card holder's bank, but usually within hours.
Why some authorizations can be voided or incrementally adjusted, and others can not be?
1) Only Visa allow any voids or incremental adjustments of authorizations. All other credit card types must obtain new authorizations.
2) Sometimes, based on events with the card holders bank, our interface will not allow us to void or incrementally adjust an authorization. The only way to do this is to call your merchant account via the phone and have them do so manually. We are not sure why these intermittent bank issues exist via an electronic gateway (never been a good explanation when we've asked), but your merchant account representative works on a direct basis with the card network and they can always do it.