I follow these instructions to install on Ubuntuhttps://github.com/opencast/pyCA/blob/main/docs/install/debian-based.rst
when I run apt update
The following signatures were invalid: EXPKEYSIG 4293B7B1EFDEB3DF PyCA Signing Key (Signing Key for PyCA Debian Repository) opencast...@elan-ev.de
and so I cannot install packages from the repository mentioned in the installation instructions.
I tried to email the address shown above so they update the PGP key, but there is no answer. I also emailed the author of this software with the same result.