Not sure if you have already solved this or not but I am having a different issue with this Add-on, so I'm writing my own and will release it soon.
Few basic troubleshooting steps:
1) Try to create JIRA manually using any other application or even chrome browser extension like Postman.
2) Check if the user you are using has the right/permission to create the ticket.
3 and the main) Check if your organization allows the request with SSL_Certificate validation = False as far as I know, this add-on has disabled SSL Validation.
4) If not you can remove the disable part from the script and add your certificate path instead to verify.
With all these checks, I think you would be good to go.
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