How to add private Composer repo to Satis with Gitlab group token?

Question

I am using Satis for my Composer repos together with Gitlab. This works in terms of open projects. So without the second repositories line it is working. As soon as I add the second line it keeps asking for credentials. The auth is a deploy username and password from the group. This works in terms of accessing the repo. This put together it not working anymore...

{
  "name": "vendor/packages",
  "homepage": "https://packages.vendor.com",
  "description": "All vendor packages",
  "repositories": [
        { "name": "vendor/my-open-package", "type": "vcs", "url": "https://gitlab.com/vendor/my-open-package.git" }
        { "name": "vendor/my-private-package", "type": "vcs", "url": "https://gitlab.com/vendor/my-private-package.git" }
  ],
  "config": {
    "http-basic": {
      "gitlab.com": {
        "username": "gitlab+deploy-token-.....",
        "password": "....."
      }
    }
  }
}

Failed to download ... file could not be downloaded (HTTP/1.1 404 Not Found)
Your credentials are required to fetch private repository metadata (...)
A token will be created and stored in "/.composer/auth.json", your password will never be stored
To revoke access to this token you can visit gitlab.com/profile/applications

The main point is that I want it to work with the group key and not a private. Any ideas how to solve this?

Thank you very much!