3rd party conversion tracking by Frank

Hi,

I am trying to use the 3rd party tracking capability as described here:

http://docs.shopify.com/support/your-store/orders/can-i-use-conversion-tracking

This is my incoming link to a test shop:

https://pens-163.myshopify.com/products/pen2?ref=4028b8814570eef901457b3405d90011

When I check on the thank-you page for the value by:

if landing_site_ref ==

or by using the order object via the webhook notification

I get null for the ref

Any ideas why?

Thanks