Nim Package Flake Issues with Importing Packages

I’m having trouble managing nim dependencies. I wrote a flake that imports nimPackages.illwil but my build command isn’t finding the dependency

{
  description = "A simple nim package";

  # Nixpkgs / NixOS version to use.
  inputs.nixpkgs.url = "nixpkgs/nixos-23.05";

  outputs = {
    self,
    nixpkgs,
  }: let
    # System types to support.
    supportedSystems = ["x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin"];

    # Helper function to generate an attrset '{ x86_64-linux = f "x86_64-linux"; ... }'.
    forAllSystems = nixpkgs.lib.genAttrs supportedSystems;

    # Nixpkgs instantiated for supported system types.
    nixpkgsFor = forAllSystems (system: import nixpkgs {inherit system;});
  in {
    # Provide some binary packages for selected system types.
    devShell = forAllSystems (system: let
      pkgs = nixpkgsFor.${system};
    in
      pkgs.mkShell {
        buildInputs = with pkgs; [
          nim
          nimlsp
          nimPackages.illwill
          git
        ];
        inputsFrom = builtins.attrValues self.packages.${system};
      });
    packages = forAllSystems (system: let
      pkgs = nixpkgsFor.${system};
      packageName = "tarotbuddy";
      inherit (pkgs) stdenv lib;
    in {
      tarotbuddy = stdenv.mkDerivation {
        name = "tarotbuddy";
        src = self;
        buildPhase = "export HOME=$(pwd); ./build.sh";
        installPhase = "mkdir -p $out/bin; install -t $out/bin tarotbuddy";
        buildInputs = with pkgs; [
          nim
          nimlsp
          git
        ];
      };

      # The default package for 'nix build'. This makes sense if the
      # flake provides only one package or there is a clear "main"
      # package.
    });
    defaultPackage = forAllSystems (system: self.packages.${system}.tarotbuddy);
  };
}

nimPackages.illwill is only available in the devshell, not in the buildinputs for the tarotbuddy derivation.

Ohhh i see, thank you