[bug]: Self hosted Gitlab Integration in Pro version

[umlumpa]

Is there an existing issue for this?

• I have searched the existing issues

Current behavior

I have deployed Plane Pro and activated the license. I want to integrate it with my self-hosted GitLab instance.
I created an application in GitLab and configured the secret, but when I set up the integration in Plane, I get a 400 Bad Request error with the payload:
"gitlab_hostname": "gitlab.com"

How can I correctly integrate Plane with my self-hosted GitLab?

Steps to reproduce

Environment

Production

Browser

Google Chrome

Variant

Self-hosted

Version

1.8.1