Use POST on /account/:id/closeSecuredCredit to close a secured-credit group. The request may target any account in the group (primary cardholder, authorized user, or collateral). The primary-cardholder credit account is closed first, which also closes any authorized-user accounts, and the collateral account is closed last. The request is rejected if the primary credit account carries an outstanding balance. A 200 with reconciling true means the collateral account is still open because an authorized-user closure has not yet been confirmed, pending authorizations remain, or a posted balance appeared after the initial balance check. Re-POST the same close until groupClosed is true. Spidr does not retry automatically, and collateral is never released while the group is still open.