If you want to use a private repository, you need to set up a token. You can easily generate a token on GitHub here.
Make sure to select the repo
scope.
More information on how to set up a token can be found on the GitHub help page.
The mod first tries to use the token from the environment, then the config file. If the token is provided through the command, it will be used for the current session and override the other methods.
You can use a (system) environment variable to set a token for all sessions.
export GITPULLER_TOKEN=<token>
CMD:
set GITPULLER_TOKEN=<token>
Powershell:
$Env:GITPULLER_TOKEN = "<token>"
You can also set up a token in the config file.
gitpuller.key=<token>
You can set up in game a token for your current session (will be lost after server restart).
/git token <token>