Examples - Create Issue
In the example below, a new issue will be created in the same project with the issue transitioned and its type will be Sub-task. The newly created issue will be linked to the issue transitioned with “is blocked by” link. Its summary will be “Subtask of {the key of the newly transitioned issue}“ and the “user picker single” field of it will be set to the assignee of the issue transitioned.
If you need to refer to the user who made the transition, use currentUser in the Jira Expression. If you use “user” instead of it, it will always refer to the app user, so the results will not be as expected.