How to add link tracking to an Abandoned Cart URL

Hello,

I am using `{{context.${metadata}.checkout_url}}` (from this support article) in an Abandoned Checkout email. 

According to the guidance in this article I should hardcode the base part of the URL and use liquid for the dynamic part. How does this work when for an Abandoned Checkout URL the full string is dynamically generated?

The email editor shows a warning: 

URL {{context.${metadata}.checkout_url | default: 'https://shop.domain.com}} failed to be assigned an LID.