Hi,
It's originally made for Jira 4.x SOAP API, and will not work at all with Jira 5 or later, as the v1 plug-in interface is no longer supported, nor work with v3, as the SOAP API wasn't mature enough then.
Development of this plug-in has completely stopped, because of these reasons. The original developer, and me as patcher/fixer, are moving on with newer Jira versions and other jobs/responsibilities.
Jira 3.13 is really old, and unsafe when used connected to the internet. For intranet use it's somewhat feasible to keep that old version.
Jira, starting with v5, has a really nice REST interface that offers all features this plug-in has, and a lot more handy-dandy stuff.
You're generally advised to upgrade to Jira 6, to get up to date.
Regards.