In order to prevent fraud, once Spotii has approved an order, the order details and order value cannot be changed.
You, the Merchant, will be able to issue partial or full refunds if items are not in stock or cannot be fulfilled for any reason. However, Spotii does not support the addition of items to an order.
The Shopper will need to place a new and separate order for the new items. Alternatively, the Shopper can cancel the previous order and raise a new order for all the items if they wish to use Spotii to pay for the new items in the same payment schedule.