For JIRA plugin to work, your site needs to have Accept remote API calls setting enabled.

To get the Jira plugin, go to Plugin manager -> More plugins and install Jira. 

Install Jira plugin

Once installed, click on Settings.

Issues from Jira will show up as tags within ManicTime. To setup a connection, you need to provide your username, password and a url to your site within Jira. You need to provide only url to site, for example:

https://manictime.atlassian.net/

Once you do, you can choose projects from which issues will be imported.

Issues will have the following format in ManicTime:
[project name], #[no. of issue - name of issue]

You can choose to also add closed issues.

You can leave starting tags empty. Whatever you write in Starting tags will be prepended to issue. For example you can write Work, then all issues will start with Work....

Once connection is established, Jira tags should be available in Add tag window, so you can use the issues in your tags.

Once you tag some time with Jira tags, you can transfer them back to Jira.