Thanks @alerque,
That’s a fantastic response. I can’t see anything in your config settings that is causing the problem. That said, your response has given me enough information to try and reproduce your issue, so I’ll try to do that and add some debugging code to see if I can figure it out.
In the meantime, if you’d like to try enabling email sign-up (you don’t even have to configure a SMTP server), that might eliminate some possible causes of the issue. You can do this by setting DisableEmailSignUp to false and if you want to skip the SMTP server setup, set ByPassEmail to true in your config file.
The fact that the API call to /teams/create_with_sso/gitlab is returning the 502/503 errors is weird and has me thinking the problem might just be reaching any of the Mattermost APIs at all, and possibly nothing to do with the link between GitLab and Mattermost. So if email sign-up doesn’t work either then that all but confirms that is the problem.