How do I show the sold-out badge on Shopify?

One option to add a sold-out badge to your out-of-stock items is through coding. But if you are not into technical dealing, you can use an app called Badgify. This app allows you to create customized badges for your products. Note that there is no automatic process of putting the sold-out badge. You must keep track of the inventory and put the sold-out badge where required. You can test this app free of cost on your Shopify store for 7 days before you decide to purchase it.