Hello @Wild Mustard,
Welcome to the Klaviyo Community!
Because the Venue theme is a custom built one, additional adjustment to the Klaviyo back in stock code or the theme code may be necessary to get this feature to work. At this time Klaviyo’s back in stock feature is only supported out of the box for standard free Shopify themes. You can see the basic free themes that are support listed in the Back in Stock Styling Code Snippets for Free Shopify Themes Help Center articles.
Theme developers are not required to follow some basic guidelines that allow our back-in-stock feature to function. Therefore we are not able to offer custom solutions for custom themes. Sometimes the theme developer will be able to help with this implementation or you can reach out to one of our many accredited Partners here: https://klaviyo.partnerpage.io/
If you end up working with a developer, you also have the option to build a fully customized solution. Our Back In Stock feature works by sending an event metric into Klaviyo which triggers a flow. You just need to send the Variant ID, Product ID, and email address. All of this can be custom-built using our open API to work with your website. If this was a viable route for you, I would suggest reviewing our Set Up Back in Stock via API article.
I hope this helps!
David