This is the documentation of JSU for Jira Cloud. If you are using JSU on Jira Server/Data Center, you can find the documentation here.
The 'Fields Required' checks whether values for specified fields are set for a given transition.
You must select mandatory fields, when configuring the transition. For example:
A workflow is configured so that the 'Ready for Review' transition has the 'Fields Required' check where the 'Reviewer' is mandatory. It will then copy the Reviewer to the Assignee, assigning the issue to the reviewer.
Supported Field Types
In its different modules (especially those for workflows), the JSU app supports many different field types. System fields, as well as custom fields.
However you should be aware, that not all field types or all combinations are supported. We think we cover the most important field types and are still continuously adding and improving which, and how different field types are supported. But the one you need might not work (yet).
We recommend that you test JSU with fields to see if it is compatible with your system. Our evaluation license gives you 30 days free trial.