@ Pat Garner
Your contribution was the reason for me to register at this forum, because I lost many hours till now by searching for the reason of this problem.
The mess is, that with the starting page you get the NOTE: For security reasons .... role "manager" .... role "admin".
No hint to the necessary role "manager-gui" for using the browser to log in as manager.
(Probably it will be written somewhere in the documentation, but it shuld be mentioned on the start page.)
The documentation has the hint to necessary role "manager-script", but if you do not know, that this is not the door for using the browser, the research is in a cul-de-sac.
So thank You very much.