If you’re using the Showcase theme and have previously installed the Klaviyo app, you’re correct that you can add it to blocks on regular pages; however, the footer does not allow app blocks by default, thus it says “no apps available” when you try to add it there.
To manually add the Klaviyo embed code to your theme’s footer, follow these steps:
Copy the embed code from your Klaviyo form (it usually includes a tag and a
).
In Shopify, go to Online Store → Themes → Edit Code.
Open the file named footer.liquid (or footer-group.liquid depending on your version of Showcase).
Paste the Klaviyo code where you want the form to appear.