Desktop POS: Selecting Out-of-Stock Settings for Desktop POS
You can decide whether you and your team members have permission to sell out-of-stock store products while making sales in POS Checkout. If you enable this option, you can display "Out of stock" labels to make it easy to see a product's inventory status.

Note:
Changes to the out-of-stock settings also affect Mobile POS.
To select POS settings:
Go to POS Settings in your site's dashboard.
Set permissions for selling out of stock products:
Allow: You can sell products even if the inventory shows that they are out of stock. After a sale, your stock count becomes negative. (e.g. -1 t-shirt in stock).
Allow with permission: Anyone with permission can sell out-of-stock products.
Note: Learn how to add staff members and assign permissions.
Don't allow: Out of stock products cannot be added to the cart.
(Optional) If you selected Allow, you can click the Show out of stock labels at checkout so you can identify that you're selling an item marked as not in stock.