Returns and adjustments to orders. You can now "Add" products to a closed order.
e.g. if customer returns an item, and you issue different stock. Or simply, if you want to add a product to the order.
Go into the order, then to the Returns/Adjustments tab.
Here you can:
If you find your order is not totaling correctly, scroll down the screen further and press "refresh totals" as below screenshot: