Splits an order into separate checks. Each entry in splits is one new order, listing order item ids, or {order_item_id, quantity} to split a line's units across checks (two waters, one each). Every unit must be assigned exactly once.

The original order ends as split, and each new order records it as parent_order_id. Discounts, taxes and fees are divided so the checks add up to the original. To split a bill evenly without splitting items, take several payments with POST /pos/orders/{order_id}/payments/ instead. Requires a staff token.