Host f-droid repository on Gitlab WITHOUT repomaker?

If I use repomaker, it gives me a URL to type in the FDroid client, and it works immediately. For example
https ://repomaker.grobox.de/repos/user_“number1”/repo_“number2”/repo
But if I use this fdroid nightly command or fdroid deploy even if I configure servergitmirrors and identity_file, I can’t access this repo from the client, no matter which URL I try.
I tried
https ://github.com/“username”/“reponame”
https ://github.com/“username”/“reponame”/fdroid/repo
https ://raw.githubusercontent.com/“username”/“reponame”/master/fdroid/repo/

I set
servergitmirrors = ‘https://github.com/“username”/“reponame”

I’d be thankful for any suggestions!