On any product page:

  1. Click the Inventory tab
  2. Select Track inventory for this product
Inventory tracking

Inventory Settings

  1. Set a current stock level for your product
  2. Set a stock level you would wish to be notified of
  3. Toggle to allow purchases when the stock level is zero

Allowing purchases when stock level reaches zero

If you toggle Allow purchase when stock level reaches zero ensure you can fulfill the order.