Users are not able to login to Relution

I have installed Relution via App Center. I can see and set the Relution checkbox in UCS Management Console when editing the user.

That does not seem to have any effect. The user is not able to login to Relution.

There is a file /var/lib/univention-appcenter/apps/relution/relution.env that has a variable LDAP_SYNCINTERVAL=12h which is commented out.
And the LDAP_USER_BASE variable is empty.

According to Relution Documentation for LDAP integration there should be an application.yml file. But I could not find that file within the Relution Docker Container.

Anybody successfully running Relution on UCS?