If an order is placed that is out of stock, it will be flagged as "needs action" in the dashboard. When clicked, there will be more details stating which action is specifically required.
We will put the item in production as soon as it is in stock, normally within the next 28 days. However, if you or your customer do not wish to wait, you can replace the item with a similar product. It may be advisable to contact your customer to discuss product replacements.
Finally, it is also possible to simply delete the order.