I guess the old download URL is not working anymore ?

Rust Server Installer is downloading an older update.

If you see an OXIDE.txt in your server install location, I'd recommend reading it. We deprecated that old URLs at https://github.com/OxideMod/Oxide/releases months ago and are no longer updating them.

If you are getting an older build, then I'm not sure where the tool you are using is pulling from, as the builds are up-to-date on our site and GitHub.

Well, I used RSI for months now and the last update still worked, so don't know what's changed since the last one ;-)

The only thing that has changed on our end is that https://github.com/OxideMod/Oxide/releases is not longer updated. We moved to the new site and have been providing direct links via it for the past few months, which you can find via the Games tab at the top of our site here.