PE GitLab WebHook does not work

[LinuxDan]

Hi, folks.

I am fighting with a PE 2019.1 instance to get Code Manager talking to GitLab and failing miserably.

I followed https://puppet.com/docs/pe/2019.1/code_mgr_webhook.html#triggering-code-manager-with-a-webhook to set it up.  I disabled SSL verification and enabled the "Allow outbound requests to the local network" settings

 

I created an authentication token and set up the URL as directed:

https://code-manager.example.com:8170/code-manager/v1/webhook?type=gitlab&token=<TOKEN>

HOWEVER, when I test it from GitLab, I get an OOPS 500 error on the GUI and an error in the gitlab-rails/production.log saying 

Net::HTTPFatalError (503 "Service Unavailable")

 If I change the "https" to "http", the test completes, but I get a 404 Network Error in the response from Puppet to GitLab, saying that the hostname of the Puppet Server could not be resolved by DNS.  The full FQDN is in both DNS and the hosts files of both servers.

Additional info:

Both servers running on CentOS 7.7, recently patched.

Gitlab is v12.4.0-ee

Any clues would be greatly appreciated.