Mirroring Help

Hello ,
Am using private repo on both GitLab and Github
Am looking to keep both GitLab and Github (private repo) in synk using mirroring option in settings on GitLab
I made an empty private repo on GitLab and added its git link to mirroring screen and selected Push as i am using GitLabas main source (code should flow from GitLab ->Github ) and selected authentication as password but it gives error as cant find repository .
Am i missing out something ?