Hello I followed instruction from https://puredata.info/docs/faq/debian. I added "deb http://apt.puredata.info/releases stable main" in /etc/apt/sources.list. I used the stable keyword instead of testing because adding "deb http://apt.puredata.info/releases testing main" (as specified in https://puredata.info/docs/faq/debian) yields some errors. There is indeed no testing directory in http://apt.puredata.info/releases/dists/. I then did both "sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-key 9f0fe587374bbe81" and "sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-key D63D3D09C39F5EEB".

When I do "sudo apt update", I get this error at the end: [...] Ign:3 http://apt.puredata.info/releases stable InRelease [...] Get:5 http://apt.puredata.info/releases stable Release [4870 B] [...] Get:7 http://apt.puredata.info/releases stable Release.gpg [904 B] Ign:7 http://apt.puredata.info/releases stable Release.gpg [...] W: GPG error: http://apt.puredata.info/releases stable Release: The following signatures were invalid: EXPKEYSIG 9F0FE587374BBE81 Hans-Christoph Steiner hans@guardianproject.info E: The repository 'http://apt.puredata.info/releases stable Release' is not signed. N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details.

Is it a known problem? Did I make a mistake somewhere?

Thank you for your time.

Best regards, Johan Mazel