error:
       … while evaluating the attribute 'drvPath'
         at «github:NixOS/nixpkgs/170ad806965c0046fb97f0d823deba0a61834aac?narHash=sha256-41upEYWDix%2BZruxPn80QHtHe304w3RHWY5RvIpw/kPg%3D»/lib/customisation.nix:415:11:
          414|         // {
          415|           drvPath =
             |           ^
          416|             assert condition;

       … while calling the 'derivationStrict' builtin
         at «nix-internal»/derivation-internal.nix:37:12:
           36|
           37|   strict = derivationStrict drvAttrs;
             |            ^
           38|

       … while evaluating the option `driverConfigurationFile':

       … while evaluating the option `driverConfiguration.vms.server.start_script':

       … while evaluating definitions from `/nix/store/qcn8cgndcms1l0py9sff5i9n73m9z2j9-source/nixos/lib/testing/driver-configuration.nix':

       … while evaluating the option `nodes.server.system.build.toplevel':

       … while evaluating definitions from `/nix/store/qcn8cgndcms1l0py9sff5i9n73m9z2j9-source/nixos/modules/system/activation/top-level.nix':

       … while evaluating the option `nodes.server.warnings':

       … while evaluating definitions from `/nix/store/qcn8cgndcms1l0py9sff5i9n73m9z2j9-source/nixos/modules/system/boot/systemd.nix':

       … while evaluating the option `nodes.server.systemd.services.vault.serviceConfig':

       … while evaluating definitions from `/nix/store/qcn8cgndcms1l0py9sff5i9n73m9z2j9-source/nixos/modules/services/security/vault.nix':

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: Refusing to evaluate package 'vault-2.0.3' in /nix/store/qcn8cgndcms1l0py9sff5i9n73m9z2j9-source/pkgs/by-name/va/vault/package.nix:70 because it has an unfree license (‘bsl11’)
       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: When using `nix shell`, `nix build`, `nix develop`, etc with a flake,
                then pass `--impure` in order to allow use of environment variables.

       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) [
             "vault"
           ];
         }

       c) For `nix-env`, `nix-build`, `nix-shell` or any other Nix command you can add
         { allowUnfree = true; }
       to ~/.config/nixpkgs/config.nix.