Link to Case in Auto Response Email when Case created from Email to Case Workflow

I am trying to make my Acknowledgement of Service Request email provide a link to the case that was created when they send an email to our help desk address. I have a custom field that gets populated on the case that contains the link. However, when I add this field to the email template it does not show up on the auto response email.

My flow is like this:

Customer sends email to help desk --> CRM creates case from email --> CRM sends auto response email confirming creation of the case.

All of this works, minus the link showing up in the email. It's blank even though I specify the field in the email template. All other fields I am using on the case show up if I place them in the email.

Does anyone have any idea why the link does not show up?