[akaunting] Installation according to tutorial does not work - Internal Error 500

I followed the instructions at https://lab.uberspace.de/guide_akaunting.html on my Uberspace - without success. Unfortunately, the source of the error could not be found

After the tutorial installation, the Internal Error 500 from Uberspace followed. The domain conforms to the following scheme: sub.sub.domain.tld /auth /user