Which ports/ Urls does Trello use to identify public facing Jira Instance

[Deon Petrus Meyer]

Hi everybody

We've got an on-prem Jira Server instance, we'd like to hook up to Trello cloud. We've installed the Jira Connector addon for Jira Server and saw that it creates an applink to a cloud-based url used for integration (jira-trello-integration.us-east-1.prod.public.atl-paas.net)

Because our server is onprem (its on our intranet as well), its not publicly exposed to the internet. We do, however, use 3rd party provider to make the site publicly accessible. 

Our Jira instance can access trello.com but when using the Jira Powerup for Trello, it can't find our server

Does anybody know which online services (urls) and ports it uses to do this lookup? If we can open up those ports and urls, then Trello should be able to recognise our instance without us having to expose our entire instance to the internet.