When doing an email template for ATS, the tag for applicant code would be [[Applicant Code]].
📌Note: Type the tag manually instead of copying and pasting it or use the paste plain text icon from the tools.
You can add a link in the email template as you add the text.
📌Note: You won't be able to query on that external link as you can't report on information that is recorded outside of PeopleHr.