Here is the quick guide to fixing this and getting your dashboard back online. Why is this happening?
This error happens because your system’s package manager (APT) requires a digital signature to verify that the software you're downloading is authentic and hasn't been tampered with. If the Webmin GPG key is missing or expired, Ubuntu/Debian will block the update for security reasons.
If you’re managing a Linux server and trying to install or update Webmin, seeing the error can be a frustrating roadblock.
Modern Linux distributions are strict about "Unsigned Repositories." When you added the Webmin repo to your sources.list , your system expected a matching . Without that key, APT throws the "not signed" or "Insecure" error and refuses to download the packages. How to Fix It (Step-by-Step) 1. Import the Webmin GPG Key