diff --git a/DbFirst.BlazorWebApp/Services/ApiClientHelper.cs b/DbFirst.BlazorWebApp/Services/ApiClientHelper.cs
new file mode 100644
index 0000000..8c803d4
--- /dev/null
+++ b/DbFirst.BlazorWebApp/Services/ApiClientHelper.cs
@@ -0,0 +1,60 @@
+using System.Net;
+using System.Net.Http.Json;
+
+namespace DbFirst.BlazorWebApp.Services;
+
+internal sealed class ProblemDetailsDto
+{
+    public string? Type { get; set; }
+    public string? Title { get; set; }
+    public string? Detail { get; set; }
+}
+
+internal static class ApiClientHelper
+{
+    public static async Task<string> ReadErrorAsync(HttpResponseMessage response)
+    {
+        string? problemTitle = null;
+        string? problemDetail = null;
+
+        try
+        {
+            var problem = await response.Content.ReadFromJsonAsync<ProblemDetailsDto>();
+            if (problem != null)
+            {
+                problemTitle = problem.Title;
+                problemDetail = problem.Detail ?? problem.Type;
+            }
+        }
+        catch { }
+
+        var status = response.StatusCode;
+        var reason = response.ReasonPhrase;
+        var body = await response.Content.ReadAsStringAsync();
+
+        string? detail = problemDetail;
+        if (string.IsNullOrWhiteSpace(detail) && !string.IsNullOrWhiteSpace(body))
+            detail = body;
+
+        return status switch
+        {
+            HttpStatusCode.BadRequest => $"Eingabe ungültig{FormatSuffix(problemTitle, detail, reason)}",
+            HttpStatusCode.NotFound => $"Nicht gefunden{FormatSuffix(problemTitle, detail, reason)}",
+            HttpStatusCode.Conflict => $"Konflikt{FormatSuffix(problemTitle, detail, reason)}",
+            HttpStatusCode.Unauthorized => $"Nicht autorisiert{FormatSuffix(problemTitle, detail, reason)}",
+            HttpStatusCode.Forbidden => $"Nicht erlaubt{FormatSuffix(problemTitle, detail, reason)}",
+            HttpStatusCode.InternalServerError => $"Serverfehler{FormatSuffix(problemTitle, detail, reason)}",
+            _ => $"Fehler {(int)status} {reason ?? string.Empty}{FormatSuffix(problemTitle, detail, reason)}"
+        };
+    }
+
+    private static string FormatSuffix(string? title, string? detail, string? reason)
+    {
+        var parts = new List<string>();
+        if (!string.IsNullOrWhiteSpace(title)) parts.Add(title);
+        if (!string.IsNullOrWhiteSpace(detail)) parts.Add(detail);
+        if (parts.Count == 0 && !string.IsNullOrWhiteSpace(reason)) parts.Add(reason);
+        if (parts.Count == 0) return string.Empty;
+        return ": " + string.Join(" | ", parts);
+    }
+}
\ No newline at end of file
diff --git a/DbFirst.BlazorWebApp/Services/CatalogApiClient.cs b/DbFirst.BlazorWebApp/Services/CatalogApiClient.cs
index 1c4590a..b928508 100644
--- a/DbFirst.BlazorWebApp/Services/CatalogApiClient.cs
+++ b/DbFirst.BlazorWebApp/Services/CatalogApiClient.cs
@@ -34,7 +34,7 @@ public class CatalogApiClient
             return ApiResult<CatalogReadDto?>.Ok(payload);
         }
 
-        var error = await ReadErrorAsync(response);
+        var error = await ApiClientHelper.ReadErrorAsync(response);
         return ApiResult<CatalogReadDto?>.Fail(error);
     }
 
@@ -46,7 +46,7 @@ public class CatalogApiClient
             return ApiResult<bool>.Ok(true);
         }
 
-        var error = await ReadErrorAsync(response);
+        var error = await ApiClientHelper.ReadErrorAsync(response);
         return ApiResult<bool>.Fail(error);
     }
 
@@ -58,68 +58,9 @@ public class CatalogApiClient
             return ApiResult<bool>.Ok(true);
         }
 
-        var error = await ReadErrorAsync(response);
+        var error = await ApiClientHelper.ReadErrorAsync(response);
         return ApiResult<bool>.Fail(error);
     }
-
-    private static async Task<string> ReadErrorAsync(HttpResponseMessage response)
-    {
-        string? problemTitle = null;
-        string? problemDetail = null;
-
-        try
-        {
-            var problem = await response.Content.ReadFromJsonAsync<ProblemDetailsDto>();
-            if (problem != null)
-            {
-                problemTitle = problem.Title;
-                problemDetail = problem.Detail ?? problem.Type;
-            }
-        }
-        catch
-        {
-        }
-
-        var status = response.StatusCode;
-        var reason = response.ReasonPhrase;
-        var body = await response.Content.ReadAsStringAsync();
-
-        string? detail = problemDetail;
-        if (string.IsNullOrWhiteSpace(detail) && !string.IsNullOrWhiteSpace(body))
-        {
-            detail = body;
-        }
-
-        if (status == HttpStatusCode.Conflict)
-        {
-            return "Datensatz existiert bereits. Bitte wählen Sie einen anderen Titel.";
-        }
-        if (status == HttpStatusCode.BadRequest && (detail?.Contains("CatTitle cannot be changed", StringComparison.OrdinalIgnoreCase) ?? false))
-        {
-            return "Titel kann nicht geändert werden.";
-        }
-
-        return status switch
-        {
-            HttpStatusCode.BadRequest => $"Eingabe ungültig{FormatSuffix(problemTitle, detail, reason)}",
-            HttpStatusCode.NotFound => $"Nicht gefunden{FormatSuffix(problemTitle, detail, reason)}",
-            HttpStatusCode.Conflict => $"Konflikt{FormatSuffix(problemTitle, detail, reason)}",
-            HttpStatusCode.Unauthorized => $"Nicht autorisiert{FormatSuffix(problemTitle, detail, reason)}",
-            HttpStatusCode.Forbidden => $"Nicht erlaubt{FormatSuffix(problemTitle, detail, reason)}",
-            HttpStatusCode.InternalServerError => $"Serverfehler{FormatSuffix(problemTitle, detail, reason)}",
-            _ => $"Fehler {(int)status} {reason ?? string.Empty}{FormatSuffix(problemTitle, detail, reason)}"
-        };
-    }
-
-    private static string FormatSuffix(string? title, string? detail, string? reason)
-    {
-        var parts = new List<string>();
-        if (!string.IsNullOrWhiteSpace(title)) parts.Add(title);
-        if (!string.IsNullOrWhiteSpace(detail)) parts.Add(detail);
-        if (parts.Count == 0 && !string.IsNullOrWhiteSpace(reason)) parts.Add(reason);
-        if (parts.Count == 0) return string.Empty;
-        return ": " + string.Join(" | ", parts);
-    }
 }
 
 public record ApiResult<T>(bool Success, T? Value, string? Error)
@@ -128,9 +69,3 @@ public record ApiResult<T>(bool Success, T? Value, string? Error)
     public static ApiResult<T> Fail(string? error) => new(false, default, error);
 }
 
-internal sealed class ProblemDetailsDto
-{
-    public string? Type { get; set; }
-    public string? Title { get; set; }
-    public string? Detail { get; set; }
-}
diff --git a/DbFirst.BlazorWebApp/Services/MassDataApiClient.cs b/DbFirst.BlazorWebApp/Services/MassDataApiClient.cs
index 6854dce..4735881 100644
--- a/DbFirst.BlazorWebApp/Services/MassDataApiClient.cs
+++ b/DbFirst.BlazorWebApp/Services/MassDataApiClient.cs
@@ -45,27 +45,10 @@ public class MassDataApiClient
             return ApiResult<MassDataReadDto?>.Ok(payload);
         }
 
-        var error = await ReadErrorAsync(response);
+        var error = await ApiClientHelper.ReadErrorAsync(response);
         return ApiResult<MassDataReadDto?>.Fail(error);
     }
 
-    private static async Task<string> ReadErrorAsync(HttpResponseMessage response)
-    {
-        try
-        {
-            var problem = await response.Content.ReadFromJsonAsync<ProblemDetailsDto>();
-            if (problem != null && !string.IsNullOrWhiteSpace(problem.Title))
-                return problem.Detail ?? problem.Title ?? response.ReasonPhrase ?? "Unbekannter Fehler";
-        }
-        catch { }
-
-        var body = await response.Content.ReadAsStringAsync();
-        if (!string.IsNullOrWhiteSpace(body))
-            return body;
-
-        return $"Fehler {(int)response.StatusCode} {response.ReasonPhrase}".Trim();
-    }
-
     public async Task<MassDataReadDto?> GetByCustomerNameAsync(string customerName)
     {
         if (string.IsNullOrWhiteSpace(customerName))