To connect with OpenID Connect, you must be registered on the authentication server AND on the application. Both entries must be made with an identical login.
You do not have credentials to log in with the authentication server? Please signon there.
Subsequently, to log in OpenID Connect:
enter the e-mail or the nickname with which you are registered,
leave the password blank, or empty it if it has been pre-filled,
press the button.
You are then transferred to the authentication server, which will ask you for your password.