I get an Error when i run "sudo apt-get update":

An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://repo.solid-build.xyz ./ Release: The following signatures were invalid: KEYEXPIRED 1508672008 Failed to fetch https://repo.solid-build.xyz/debian/jessie/bsp-imx6/./Release Some index files failed to download. They have been ignored, or old ones used instead.

I guess i need a new key, but how can i get it? Thx for any help.

System: Debian GNU/Linux 8.7 (jessie) with MATE 1.8.1 Desktop Environment

I tried:

apt-key list

and found 3 expired keys, so i tried:

apt-key adv --keyserver keys.gnupg.net --recv-keys [KEY]

I did this with all 3 expired keys but again with apt-key list they didnt changed. What am i missing here?