Get rid of residual MatterMost crap on my system

Questions
1

I removed MatterMost a while ago. But I keep getting the following error and I can’t find a solution to resolve it other than getting the MatterMost keys. But I don’t want that. I want to get rid of the code that is making linux even look for it.

W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://deb.packages.mattermost.com stable InRelease: The following signatures were invalid: EXPKEYSIG F8F2C31744774B28 Mattermost Build dev-ops@mattermost.com
W: Failed to fetch https://deb.packages.mattermost.com/dists/stable/InRelease The following signatures were invalid: EXPKEYSIG F8F2C31744774B28 Mattermost Build dev-ops@mattermost.com

2

How did you remove it? My thought is that something was left behind in /etc/apt/sources.list.d during the uninstall of MatterMost. In a terminal do “cd /etc/apt/sources.list.d”, then “ls”. What do you see in that directory? If there’s something obviously related to MatterMost, that may be the culprit.

If your MatterMost install was a flatpak, in the terminal run “flatpak list --all”.