Add Shopify product tags to Klaviyo Back in Stock event payload

We use STOQ Back in Stock alerts with Klaviyo and need a way to distinguish between a genuine restock and a product becoming available for preorder.

Our preorder workflow uses positive Shopify inventory. A product may initially be out of stock, allowing customers to subscribe through STOQ's Back in Stock widget. When we later open the product for preorder, we increase the inventory from 0 to a positive quantity and add the Shopify product tag preorder.

Because the inventory becomes positive, STOQ triggers the Back in stock alert (STOQ) event. However, in this case the product is not actually back in stock — it is available for preorder.

We would like Shopify product tags to be included in the Klaviyo event payload, for example:

product_tags: ["preorder"]

Ideally, this should also be available in Back in Stock reminder events.

This would allow us to create a Klaviyo trigger split such as:

product_tags contains preorder → send a preorder-specific email

Otherwise → send our normal Back in Stock email.

This would let us keep our current preorder workflow while ensuring customers receive the correct message.