Please follow the instructions below to enable the pre-order button #
When you sell out of a quantity of an item, by default Shopify won’t allow customers to purchase that item until you adjust the inventory levels to add more stock. You can change the default to allow customers to buy out-of-stock items from the Inventory section of a product.
You might want to allow customers to buy out-of-stock items for any of the following reasons:
- You have products available for pre-order.
- You have stock coming soon and you want to continue selling before it arrives.
- You want to sell first and then order supplies later.
- You aren’t tracking the actual inventory quantity in Shopify.
Enable the pre-order button from the theme customizer #
Go to product page > Buy buttons > Show pre-order button