Upgrading from High Sierra not working on 2015 15" Macbook Pro.

I have tried many ways to update my MacBook Pro from High Sierra--even the App Store update page is all messed up. No option to update OS visible. The links on the Apple help page "how to upgrade an old OS" don't work. Not available in the US. When I reboot in restore the only option is High Sierra which I already re-uploaded.