Show pre-order buttons when inventory is equal or less than 0

The Pre-order button will automatically replace the “Add-to-cart” button on the product detail page when the inventory is out of stock.

Steps to manage:

1. From the admin page of the app, click on ” Single product” tab
2. Click ” Add product“
3. Select any available product that you want to add on pre-order
4. Enable pre-order status
5. Select Pre-order start condition with the start quantity equal to or less than 0

6.Set up “ Overselling settings “: Automatically turn on “Continue selling when out of stock” for all “Track quantity” products

Or you can enable ”  Continue selling when out of stock”  in each of pre-order products in the Product admin page 

7.Click Save to finish

8.Check out the result at the front-end store