diff --git a/DbFirst.BlazorWebApp/Components/MassDataGrid.razor b/DbFirst.BlazorWebApp/Components/MassDataGrid.razor
index 249026f..cc8686a 100644
--- a/DbFirst.BlazorWebApp/Components/MassDataGrid.razor
+++ b/DbFirst.BlazorWebApp/Components/MassDataGrid.razor
@@ -305,18 +305,17 @@ else
             Category = editModel.Category,
             StatusFlag = editModel.StatusFlag
         };
-        try
+
+        var result = await Api.UpsertAsync(dto);
+        if (!result.Success)
         {
-            var saved = await Api.UpsertAsync(dto);
-            infoMessage = editModel.IsNew ? "MassData angelegt." : "MassData aktualisiert.";
-            focusedRowKey = saved.Id;
-            await LoadPage(pageIndex);
-        }
-        catch (Exception ex)
-        {
-            errorMessage = $"Fehler beim Speichern: {ex.Message}";
+            errorMessage = result.Error ?? "Speichern fehlgeschlagen.";
             e.Cancel = true;
+            return;
         }
+        infoMessage = editModel.IsNew ? "MassData angelegt." : "MassData aktualisiert.";
+        focusedRowKey = result.Value?.Id;
+        await LoadPage(pageIndex);
     }
 
     private void AddValidationError(MassDataEditModel editModel, string fieldName, string message)
diff --git a/DbFirst.BlazorWebApp/Services/MassDataApiClient.cs b/DbFirst.BlazorWebApp/Services/MassDataApiClient.cs
index 2ee4cbe..6854dce 100644
--- a/DbFirst.BlazorWebApp/Services/MassDataApiClient.cs
+++ b/DbFirst.BlazorWebApp/Services/MassDataApiClient.cs
@@ -36,12 +36,34 @@ public class MassDataApiClient
         return result ?? new List<MassDataReadDto>();
     }
 
-    public async Task<MassDataReadDto> UpsertAsync(MassDataWriteDto dto)
+    public async Task<ApiResult<MassDataReadDto?>> UpsertAsync(MassDataWriteDto dto)
     {
         var response = await _httpClient.PostAsJsonAsync($"{Endpoint}/upsert", dto);
-        response.EnsureSuccessStatusCode();
-        var payload = await response.Content.ReadFromJsonAsync<MassDataReadDto>();
-        return payload ?? new MassDataReadDto();
+        if (response.IsSuccessStatusCode)
+        {
+            var payload = await response.Content.ReadFromJsonAsync<MassDataReadDto>();
+            return ApiResult<MassDataReadDto?>.Ok(payload);
+        }
+
+        var error = await 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)