Automation that will add a custom field value to a checklist

Im trying to create an automation that attaches a card and the custom field value after the custom field value is updated. 

Here's an example of the automation i made.

Everything looks right but when it gets to adding the item to the checklist it doesn't post the custom fields value.

Here's a screenshot showing the cards showing the custom field is updated. 

EDIT: if i were to change the automation to make a comment on a card instead of the checklist it works like it should  - the checklist would be the preferred method