invalid credential type for any passed RemoteCallback

[mathisloge]

pygit2 version: 1.14.1
Python version: 3.10.12

I'm trying to connect to the git server with via a ssh url.
e.g. remote.url is ssh://example.com:22/path/to/repo

When I'm trying to remote.fetch(callbacks=callbacks) (or any other operation like push or connect) I'm getting TypeError: invalid credential type

It doesn't matter which credential provider I pass into the RemoteCallbacks object.
For example:

keypair = pygit2.Keypair("git", "/home/myuser/.ssh/id_rsa.pub", "/home/myuser/.ssh/id_rsa", "")
callbacks = pygit2.RemoteCallbacks(keypair)

or

keypair = pygit2.UserPass("eeee", "xxx")
callbacks = pygit2.RemoteCallbacks(keypair)

or

keypair = pygit2.KeypairFromAgent("git")
callbacks = pygit2.RemoteCallbacks(keypair)

I'm getting always the following stack trace:

  File "..../site-packages/pygit2/remotes.py", line 120, in connect
    payload.check_error(err)
  File "..../site-packages/pygit2/callbacks.py", line 93, in check_error
    raise self._stored_exception
  File "..../site-packages/pygit2/callbacks.py", line 416, in wrapper
    return f(*args)
  File "..../site-packages/pygit2/callbacks.py", line 484, in _credentials_cb
    ccred = get_credentials(credentials, url, username, allowed)
  File "..../site-packages/pygit2/callbacks.py", line 579, in get_credentials
    raise TypeError("invalid credential type")

The repository is initialized with repo = Repository(discover_repository("/root/path/of/my/repo"))
With git itself I can do all the operations. So I guess that the settings are correct.

Do you have any idea which does let this operation fail?