Open the proposal and click the Delete (trash) icon in the toolbar, then confirm "Are you sure you want to delete this proposal?" — in the current version this icon is only on the proposal's own edit page, not in the Events list (the list's Actions column only has a Clone icon). Sprwt deletes the proposal record, its line items (meals, custom meals, expenses, invoice items), its status log and customer links, its contract instances, its activity log, and its uploaded files folder. Checkouts (payments) already made are only unlinked from the proposal — the underlying orders remain in the Checkouts area untouched and are not refunded automatically; refund them first from the Payments tab if needed. If you only want to hide an event, set its Status to Archived instead.