@noiob try to ssh there first and get that ip into your known_hosts before running npm?
@noiob looks like this could be caused by how old that version of npm is (https://GitHub.com/nebrius/raspi-serial/issues/8)
npm install -g npm may help? or reinstalling with the system package manager
also possible the registry moved: npm config set registry https://registry.npmjs.org
@starfall yeah it seems to be a problem with debian package versions -.- I tried switching to yarn and while I still had to add an external repo it now seems to work. Thanks fot your help!