Field code
%{issue.lastComment.author}
Field code
issue?.comments!= [] ? issue?.comments[issue?.comments?.length-1].author?.accountId : null

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

You can access the whole comment by issue.comments[0] which returns an objectissue.comments will return a list of objects.

Read

Returned valueThe Atlassian account ID of the user who entered the last comment in the issue
Output data type

TEXT

Example output557068:145e0983-5707-439c-80e4-1160dd57g114

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