How do I get the kickstart nix nvim overlay to work?

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1

I’m trying to follow the installation instructions here:

for kickstart nix nvim. Obviously I’m missing something.
Here’s my most recent attempt:

When I rebuild I just get:

       error: undefined variable 'nvim-pkg'
       at /nix/store/qnhradaa8l8v5mgs07r16b28f2fijfj3-source/configuration.nix:9:5:
            8|   environment.systemPackages = with pkgs; [
            9|     nvim-pkg # kickstart neovim
             |     ^
           10|     git # vc

clearly my overlay is not taking but I don’t know how/where to fix it