Shogun can be used to create custom pages on a Shopify store.

Integration of Discount Ninja requires that your Shogun page is based on an "Existing Layout" rather than a "Custom Layout".

This allows your Shogun page to leverage the liquid snippets injected into your theme that Discount Ninja relies on.

More information can be found here: https://getshogun.com/help/en/articles/2518739-how-do-i-embed-a-third-party-application-into-a-product-page.