Some nix options have been renamed.

config/nix.nix

@@ -4,22 +4,24 @@ let
   cfg = config.machine;
 in {
   nix = {
-    maxJobs = 4;
-    buildCores = 1;
-    autoOptimiseStore = true;
-    useSandbox = true;
     package = pkgs.nix_2_4;
-    allowedUsers = [ "root" ] ++ (map (n: n.name) cfg.administrators);
+    settings = {
+      max-jobs = 4;
+      cores = 1;
+      sandbox = true;
+      auto-optimise-store = true;
+      trusted-substituters = [
+        "https://cache.nixos.org"
+      ] ++ cfg.binaryCaches;
+      trusted-public-keys = [ (lib.fileContents "${cfg.secretPath}/hydra_cache.pub") ];
+      substituters = [
+        "https://cache.nixos.org"
+      ] ++ cfg.binaryCaches;
+      allowed-users = [ "root" ] ++ (map (n: n.name) cfg.administrators);
+    };
     extraOptions = ''
       build-timeout = 86400  # 24 hours
       experimental-features = nix-command flakes
     '';
-    binaryCachePublicKeys = [ (lib.fileContents "${cfg.secretPath}/hydra_cache.pub") ];
-    trustedBinaryCaches = [
-      "https://cache.nixos.org"
-    ] ++ cfg.binaryCaches;
-    binaryCaches = [
-      "https://cache.nixos.org"
-    ] ++ cfg.binaryCaches;
   };
 }