Wholesale-replace the ordered tiers of approvers on an existing approval flow — the V3 equivalent of rebuilding the flow's structure from an external HRIS. The flow must be in pending status; resolved (approved or rejected) flows cannot be modified. The new array's index becomes each group's sort_order, each approver entry must identify a user by user_id, email, or employee_id, and the same user cannot appear in more than one group. To swap a single approver inside a group without touching the rest of the flow use PUT /v3/approver_groups/{id}/replace_approver; to flip the flow between sequential and parallel use PATCH /v3/approval_flows/{id}.