A customer can request a refund directly from the Done step of the tip flow, with an optional reason. From a Dashboard tip's detail page, a manager can also request a refund on a completed tip that doesn't already have an active refund in progress.
The Refunds Queue on Dashboard → Payments lists every request, filterable by status: Pending, Approved, Rejected, or Completed. Refund history for a specific tip is always visible on that tip's detail page.