Problem with Using a Shopify Order Metafield ( invoice_url ) in a Klaviyo Flow Email

Hi everyone,

I’m trying to include a PDF invoice link in a Klaviyo shipping confirmation Flow email, where the URL is different for each Shopify order.

This is my Setup:

• For every Shopify order with status fulfilled, there is an Order metafield:
  • Namespace: momomo
  • Key: invoice_url
  • Type: single_line_text_field
  • Value: a full PDF URL (https://…pdf)
• The metafield exists on the order and can be retrieved via the Shopify Admin API, e.g.:

/orders/{order_id}/metafields.json

Goal: Use the value of momomo.invoice_url as a dynamic variable in a Klaviyo Flow email, for example:

“Download your invoice (PDF)”

Problem

• The metafield is not available in Klaviyo’s Fulfilled Order event payload (event.extra)
• In Shopify Flow → “Update order metafield”, the dropdown only shows token_gated_order_metafields, not my custom metafield
• Referencing it directly in Klaviyo like:

{{ event.extra.metafields.momomo.invoice_url }}

does not work (value is empty / preview breaks)

Question

What is the recommended / cleanest way to make a Shopify order metafield (like invoice_url) available in a Klaviyo Flow email?

• Is Shopify Flow the right approach to copy it into a place Klaviyo can read?
• Or is a middleware / webhook required?
• Has anyone implemented this reliably without building a custom Shopify app?

Thanks a lot