Product Block pointing to shopify store and not headless store

Hi @ChrisTough ,

Welcome to the Community. I see that you stated you are on a "headless Shopify integration". 
If that is the case and you don't wish to have the integration installed, you would need to create a Custom Catalog in order to create a Product Feed. After creating the catalog you should be able to use Klaviyo’s Product Recommendation, Product Block, and Catalog Lookup Tag features. To learn how to learn how to sync a custom catalog feed to Klaviyo, please refer to our Developer Guide here.

Make sure to create a Custom Catalog. As you read the attached documentation, a few things of note:

• The first step is to sync your custom catalog to Klaviyo; you will be asked to specify a URL to fetch products from. This custom catalog feed must be either an XML or JSON feed, and we only accept data 1 node deep (unless the feed is hosted by Google Merchant Feeds).
• There are certain required fields for each catalog item, as well as some optional but recommended fields, so you can maximize the use of your catalog in Klaviyo.
• Our current default item limit for a custom feed is 25K items - if your catalog contains more than 25K items, let us know what the maximum count is before adding the feed to the account and we will raise this limit for you.
• Once you have your product catalog synced, I will need to complete one final step on my end before you can set up a Product Feed using this new source.

 
You can also take a look at these helpful documentations:

• Sync a Custom Catalog Feed to Klaviyo
• Use Custom Catalog Data in Emails