Can't install material shell extension

I’m trying to install material shell which is only in unstable right now.

I’m using the guide from the wiki to install a package from unstable.

I am able to install gnome extensions from 20.09 with no errors.
I am able to install packages from unstable with no errors.
When I try to install “unstable.gnomeExtensions.material-shell” I get the following build error:

building Nix...
building the system configuration...
error: attribute 'material-shell' missing, at /cfg/configuration.nix:102:5
(use '--show-trace' to show detailed location information)

I’ve tried installing through both environment.systemPackages in my configuration.nix and my home.packages in my home.nix.

Do I need to use a different package name to get this to work?

For those that may find this in the future resolution was that I was using an older repo for the unstable repository: nix - NixOs Attribute Error with unstable package on stable release - Unix & Linux Stack Exchange