Apt-get update problem

Hey! What I’ve done wrong?
Tried to delete the old repo source and set new one using this instruction https://docs.loraserver.io/install/install/, Got an issue while updating my packages by apt-get update…

Reading package lists… Done
W: The repository ‘https://repos.loraserver.io/linuxmint serena Release’ does not have a Release file.
N: Data from such a repository can’t be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch https://repos.loraserver.io/linuxmint/dists/serena/testing/binary-amd64/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.

What is the correct link for ubuntu-like distros?

I was able to fix it by myself. The correct link is here:
It seems that you have changed the link but have not changed installation instructions yet. Close this issue.