diff --git a/src/ZB.MOM.WW.ScadaBridge.InboundAPI/ParameterValidator.cs b/src/ZB.MOM.WW.ScadaBridge.InboundAPI/ParameterValidator.cs
index 75790067..f36ff743 100644
--- a/src/ZB.MOM.WW.ScadaBridge.InboundAPI/ParameterValidator.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.InboundAPI/ParameterValidator.cs
@@ -114,10 +114,78 @@ public static class ParameterValidator
             "number" => element.GetDouble(),
             "string" => element.GetString(),
             "object" => JsonSerializer.Deserialize<Dictionary<string, object?>>(element.GetRawText()),
-            "array" => JsonSerializer.Deserialize<List<object?>>(element.GetRawText()),
+            "array" => MaterializeArray(element, schema.Items),
             _ => JsonSerializer.Deserialize<object?>(element.GetRawText()),
         };
     }
+
+    /// <summary>
+    /// Materializes a JSON array to a STRONGLY-TYPED list (List&lt;string&gt;,
+    /// List&lt;long&gt;, List&lt;double&gt;, List&lt;bool&gt;) per the element schema,
+    /// rather than a <c>List&lt;object?&gt;</c> of raw <see cref="JsonElement"/>. The
+    /// raw-JsonElement form is not cleanly Akka-serializable when the parameter is
+    /// routed Central→Site, and a script writing it to a List attribute stalls when
+    /// the attribute codec tries to JSON-serialize JsonElement items. A typed list
+    /// serializes cleanly across nodes and encodes to a canonical JSON array, which
+    /// the InstanceActor decodes back to the typed list for the device write.
+    /// </summary>
+    private static object? MaterializeArray(JsonElement element, InboundApiSchema? items)
+    {
+        // When the element type is a declared scalar, build a STRONGLY-TYPED list
+        // (List<string>/long/double/bool) — the cleanest form to route Central→Site
+        // and to encode to a canonical JSON array for a List attribute write.
+        switch (items?.Type)
+        {
+            case "integer":
+            {
+                var list = new List<long>(element.GetArrayLength());
+                foreach (var e in element.EnumerateArray()) list.Add(e.GetInt64());
+                return list;
+            }
+            case "number":
+            {
+                var list = new List<double>(element.GetArrayLength());
+                foreach (var e in element.EnumerateArray()) list.Add(e.GetDouble());
+                return list;
+            }
+            case "boolean":
+            {
+                var list = new List<bool>(element.GetArrayLength());
+                foreach (var e in element.EnumerateArray()) list.Add(e.GetBoolean());
+                return list;
+            }
+            case "string":
+            {
+                var list = new List<string>(element.GetArrayLength());
+                foreach (var e in element.EnumerateArray())
+                    list.Add(e.ValueKind == JsonValueKind.Null ? string.Empty : e.GetString() ?? string.Empty);
+                return list;
+            }
+            default:
+            {
+                // No declared (or non-scalar) element type: materialize each element
+                // to its CLR value so no raw JsonElement survives (raw JsonElement is
+                // not cleanly Akka-serializable and stalls the List-attribute encode).
+                var list = new List<object?>(element.GetArrayLength());
+                foreach (var e in element.EnumerateArray()) list.Add(MaterializeJsonValue(e));
+                return list;
+            }
+        }
+    }
+
+    /// <summary>Recursively converts a <see cref="JsonElement"/> to a plain CLR value
+    /// (string/long/double/bool/null, or nested List/Dictionary) — never a JsonElement.</summary>
+    private static object? MaterializeJsonValue(JsonElement e) => e.ValueKind switch
+    {
+        JsonValueKind.String => e.GetString(),
+        JsonValueKind.Number => e.TryGetInt64(out var l) ? l : e.GetDouble(),
+        JsonValueKind.True => true,
+        JsonValueKind.False => false,
+        JsonValueKind.Null => null,
+        JsonValueKind.Array => e.EnumerateArray().Select(MaterializeJsonValue).ToList(),
+        JsonValueKind.Object => e.EnumerateObject().ToDictionary(p => p.Name, p => MaterializeJsonValue(p.Value)),
+        _ => e.GetRawText(),
+    };
 }
 
 /// <summary>