diff --git a/csharp/App/Backend/Services/AlarmKnowledgeBase.cs b/csharp/App/Backend/Services/AlarmKnowledgeBase.cs
index 6573f36c4..15848c769 100644
--- a/csharp/App/Backend/Services/AlarmKnowledgeBase.cs
+++ b/csharp/App/Backend/Services/AlarmKnowledgeBase.cs
@@ -1,5 +1,3 @@
-using System.Collections.Frozen;
-
 namespace InnovEnergy.App.Backend.Services;
 
 /// <summary>
@@ -43,7 +41,7 @@ public static class AlarmKnowledgeBase
     // Register addresses: 0x1048 - 0x10D5
     // Recovery types: AUTO (wait), MANUAL (fix and restart), SERVICE (contact service)
 
-    private static readonly FrozenDictionary<string, DiagnosticResponse> SinexcelAlarms = new Dictionary<string, DiagnosticResponse>
+    private static readonly IReadOnlyDictionary<string, DiagnosticResponse> SinexcelAlarms = new Dictionary<string, DiagnosticResponse>
     {
         // Grid-related alarms
         ["Abnormal grid voltage"] = new()
@@ -958,12 +956,12 @@ public static class AlarmKnowledgeBase
             Causes = new[] { "Load exceeds generator capacity" },
             NextSteps = new[] { "Reduce load", "Fix the cause, then restart" }
         },
-    }.ToFrozenDictionary();
+    };
 
     // ── Growatt Alarms ───────────────────────────────────────────────────────
     // Format: "Warning XXX" or "Error XXX" or descriptive text
 
-    private static readonly FrozenDictionary<string, DiagnosticResponse> GrowattAlarms = new Dictionary<string, DiagnosticResponse>
+    private static readonly IReadOnlyDictionary<string, DiagnosticResponse> GrowattAlarms = new Dictionary<string, DiagnosticResponse>
     {
         // Warnings (200-series: PV/String)
         ["Warning 200"] = new()
@@ -1510,5 +1508,5 @@ public static class AlarmKnowledgeBase
             Causes = new[] { "Too many PV modules in series", "Cold temperature increasing Voc" },
             NextSteps = new[] { "Disconnect DC switch immediately", "Check voltage", "Reconfigure strings if needed" }
         },
-    }.ToFrozenDictionary();
+    };
 }
diff --git a/csharp/App/Backend/Services/DiagnosticService.cs b/csharp/App/Backend/Services/DiagnosticService.cs
index b2948f3de..ed0b2e30f 100644
--- a/csharp/App/Backend/Services/DiagnosticService.cs
+++ b/csharp/App/Backend/Services/DiagnosticService.cs
@@ -126,8 +126,7 @@ Reply with ONLY valid JSON, no markdown:
             };
 
             var responseText = await MistralUrl
-                .SetHeader("Authorization", $"Bearer {_apiKey}")
-                .SetHeader("Content-Type", "application/json")
+                .WithHeader("Authorization", $"Bearer {_apiKey}")
                 .PostJsonAsync(requestBody)
                 .ReceiveString();
 
@@ -147,7 +146,7 @@ Reply with ONLY valid JSON, no markdown:
         }
         catch (FlurlHttpException httpEx)
         {
-            Console.Error.WriteLine($"[DiagnosticService] HTTP error {httpEx.Response?.StatusCode}: {await httpEx.Response?.GetStringAsync()}");
+            Console.Error.WriteLine($"[DiagnosticService] HTTP error {httpEx.StatusCode}: {httpEx.Message}");
             return null;
         }
         catch (Exception ex)