Runner Register: 500 Internal Service Error when registering a Runner

I have a self-hosted instance of GitLab that uses a self-signed certificate. I am trying to register a gitlab-runner on one of my windows machines.

I have given the details such as instance, token, description and tags, however, after that it shows me an error as following
“ERROR: Registering runner… failed runner=2xoKkNki status=POST https://my.gitlabacts.instance/api/v4/runners: 500 Internal Server Error ()
PANIC: Failed to register the runner.”

I am not able to understand why this could be.

The gitLab instance version is: 14.1.2-ee