Cancel a single seller order item on an order. Order items are fully cancelled by default. Order items can be partially cancelled by using the newQuantity parameter. Note that doing a partial cancellation will cancel the original seller order item and create a new order item representing the uncancelled quantity. Fulfilled items cannot be cancelled.

Note: 'Order item' in this context specifically refers to seller order items (found at order.sellerOrders[].items[]). The top-level order items (found at order.items[]) are not modified by cancellation endpoints.