window.Shopify object null on the Post Purchase Page

Devs,

We are trying to access the window.Shopify.order object on the post purchase page. Documentation here: https://help.shopify.com/en/manual/promoting-marketing/analyze-marketing/pixel-tracking-post-purchase-page#table-heading-window says it exists. However, it is NULL when our script executes on this post purchase page.

Why?

We need the order ID, checkout token, or email. Any would work. Thanks!