Just hit this error today … is there a certificate or server issue perhaps? BTW, this is when trying to run apt update on Ubuntu,
Err:24 https://packages.graylog2.org/repo/debian stable Release
Certificate verification failed: The certificate is NOT trusted. The certificate chain uses expired certificate. Could not handshake: Error in the certificate verification. [IP: 18.214.118.253 443]
Reading package lists... Done
E: The repository 'https://packages.graylog2.org/repo/debian stable Release' no longer has a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
I had the same issue with the OVA install. If you want a quick fix, just remove the https and replace with http.
Not ideal but gets around this issue until it is resolved. Adjust the below for the branch you want to use: