Libresign --> error when signing | NC20

Dear NC community,
did someone succeed in not only installing and setting up the Libresign app together with CFSSL and successfully signing a PDF?
I am using NC20 and I have installed the dependencies including CFSSL docker container. Libresign app (2.2.1) did install nicely and I could generate a root certificate. I have registered my NC account using the app.
THen I went on and selected a PDF in the files app and tried to sign with the sidebar which always gives my an error. THe nextcloud log does not give me a clue.
I followed the setup guidance in github for LibreSign.

Anyone with a working setup?


Meanwhile things got further in the LibreSign GIthub Issues: