Field code
issue?.links[0]?.linkedIssue?.key

Links are stored in lists. Documentation on how to work with lists can be found here.

You can access the whole link by issue?.links[0]?.linkedIssue which returns an Issue object, issue?.links will return a list of objects.

Read

Returned valueThe key of the issue which the first link was obtained for, is linked to. If no linked issues are available, null is returned.
Output data type

TEXT

Example outputPRJ-5

If you still have questions, feel free to refer to our support team.