GitLab integration can't connect error

We're running the latest (1.29) version of Swaggerhub on-premise and while trying to setup GitLab integration (to an on-premise GitLab instance), I keep receiving a 'can't connect' error message when setting up the GitLab integration for an API. We have the FQDN url of our GitLab instance defined in the admin settings and it shows up as the default when setting up the integration.

I've verified that our Swaggerhub appliance can connect to GitLab successfully using Putty and the NC command. I've also verified my local laptop can connect to GitLab just fine too (over SSL for both). I also created a new PAT to use, but that part doesn't seem to matter.

Any ideas on why I'm getting what seems to be a network connectivity error but all indications are that there is?

Thanks!