Got this error after updating /etc/apt/sources.list.d/kaltura.list
and adding the new key I still get this error.
W: GPG error: http://installrepo.kaltura.org/repo/apt/debian mercury InRelease: The following signatures were invalid: AD4200615722734CBBE6C52FE7EEDECAA1174D5E
W: The repository ‘http://installrepo.kaltura.org/repo/apt/debian mercury InRelease’ is not signed.
N: Data from such a repository can’t be authenticated and is therefore potentially dangerous to use.