nixos error

txt

error: Package ‘Oracle_VM_VirtualBox_Extension_Pack-6.1.40.vbox-extpack’ in /nix/store/6k5n9v6j37g9bari1a5cj5cg6pqrdd4k-source/pkgs/applications/virtualization/virtualbox/extpack.nix:19 has an unfree license (‘virtualbox-puel’), refusing to evaluate.

       a) To temporarily allow unfree packages, you can use an environment variable
          for a single invocation of the nix tools.

            $ export NIXPKGS_ALLOW_UNFREE=1

        Note: For `nix shell`, `nix build`, `nix develop` or any other Nix 2.4+
        (Flake) command, `--impure` must be passed in order to read this
        environment variable.

       b) For `nixos-rebuild` you can set
         { nixpkgs.config.allowUnfree = true; }
       in configuration.nix to override this.

       Alternatively you can configure a predicate to allow specific packages:
         { nixpkgs.config.allowUnfreePredicate = pkg: builtins.elem (lib.getName pkg) [
             "Oracle_VM_VirtualBox_Extension_Pack"
           ];
         }

       c) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
         { allowUnfree = true; }
       to ~/.config/nixpkgs/config.nix.
(use '--show-trace' to show detailed location information)