ticketsytsem
Doesn't look like the author is supporting that plugin anymore. Which is where you should go for support.
In fact, I'd be suspicious of any plugin without a recent update. Been a lot of changes in MyBB, PHP, and database versions since 2015-06-03. All of which can impact such a project. Just because it's in extend - doesn't mean it's up-to-date. But that info is right there for you to read.
Not saying it can't be made to work. But you're probably on your own.
In fact, I'd be suspicious of any plugin without a recent update. Been a lot of changes in MyBB, PHP, and database versions since 2015-06-03. All of which can impact such a project. Just because it's in extend - doesn't mean it's up-to-date. But that info is right there for you to read.
Not saying it can't be made to work. But you're probably on your own.