After some searching, I have found a number of people raised this question in the past, but I have not found a solution that works. The closest I have found is the following:
https://jira.atlassian.com/browse/JRASERVER-33927
Essentially, I am looking to use the REST-API to convert an existing issue to a sub-task of a parent issue.
Hello @BrettDunstan
No, it’s not supported yet for the REST APIs of either Jira Server JRASERVER-27893 or Jira Cloud JRACLOUD-27893, hence the reason both feature requests are still in the Gathering Interest state.
Also, if you do a Google search for “Jira REST API convert to sub-task” you’ll see where the same question has been discussed previously.
Thanks. I have seen and read most of the posts about this issue and since they go back to 2015/2016 and earlier, I wasnt sure if there was any new development on this topic.