diff --git a/src/Altinn.Broker.API/Helpers/ValidateUseManifestFileShim.cs b/src/Altinn.Broker.API/Helpers/ValidateUseManifestFileShim.cs
new file mode 100644
index 00000000..e92df78a
--- /dev/null
+++ b/src/Altinn.Broker.API/Helpers/ValidateUseManifestFileShim.cs
@@ -0,0 +1,32 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Altinn.Broker.Helpers
+{
+    [AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
+    public class ValidateUseManifestFileShim : ValidationAttribute
+    {
+        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
+        {
+            var useManifestFileShimProperty = validationContext.ObjectType.GetProperty("UseManifestFileShim");
+            var externalServiceCodeLegacyProperty = validationContext.ObjectType.GetProperty("ExternalServiceCodeLegacy");
+            var externalServiceEditionCodeLegacyProperty = validationContext.ObjectType.GetProperty("ExternalServiceEditionCodeLegacy");
+            var useManifestFileShimValue = (bool?)useManifestFileShimProperty.GetValue(validationContext.ObjectInstance, null);
+            var externalServiceCodeLegacyValue = externalServiceCodeLegacyProperty.GetValue(validationContext.ObjectInstance, null);
+            var externalServiceEditionCodeLegacyValue = externalServiceEditionCodeLegacyProperty.GetValue(validationContext.ObjectInstance, null);
+
+            if (useManifestFileShimValue == true)
+            {
+                if (externalServiceCodeLegacyValue == null || (externalServiceCodeLegacyValue is string strValue && string.IsNullOrEmpty(strValue)))
+                {
+                    return new ValidationResult("ExternalServiceCodeLegacy must be set and not be an empty string.");
+                }
+
+                if (externalServiceEditionCodeLegacyValue == null || (externalServiceEditionCodeLegacyValue is int intValue && intValue == 0))
+                {
+                    return new ValidationResult("ExternalServiceEditionCodeLegacy must be set and not be zero.");
+                }
+            }
+            return ValidationResult.Success;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/Altinn.Broker.API/Models/ResourceExt.cs b/src/Altinn.Broker.API/Models/ResourceExt.cs
index 52888db9..0df9f4ac 100644
--- a/src/Altinn.Broker.API/Models/ResourceExt.cs
+++ b/src/Altinn.Broker.API/Models/ResourceExt.cs
@@ -1,10 +1,14 @@
 using System.Text.Json.Serialization;
 
+using Altinn.Broker.Helpers;
+
 namespace Altinn.Broker.Models;
 
 /// <summary>
 /// API input model for file initialization.
 /// </summary>
+[ValidateUseManifestFileShim]
+
 public class ResourceExt
 {
 
diff --git a/src/Altinn.Broker.Application/ConfigureResource/ConfigureResourceHandler.cs b/src/Altinn.Broker.Application/ConfigureResource/ConfigureResourceHandler.cs
index e4817d1c..35e030cc 100644
--- a/src/Altinn.Broker.Application/ConfigureResource/ConfigureResourceHandler.cs
+++ b/src/Altinn.Broker.Application/ConfigureResource/ConfigureResourceHandler.cs
@@ -61,24 +61,14 @@ public async Task<OneOf<Task, Error>> Process(ConfigureResourceRequest request,
         if (request.UseManifestFileShim is not null)
         {
             var updateManifestFileShimResult = await UpdateUseManifestFileShim(resource, request.UseManifestFileShim.Value, cancellationToken);
+            await resourceRepository.UpdateExternalServiceCodeLegacy(resource.Id, request.ExternalServiceCodeLegacy, cancellationToken);
+            await resourceRepository.UpdateExternalServiceEditionCodeLegacy(resource.Id, request.ExternalServiceEditionCodeLegacy, cancellationToken);
+            
             if (updateManifestFileShimResult.IsT1)
             {
                 return updateManifestFileShimResult.AsT1;
             }
         }
-        if (request.UseManifestFileShim == true)
-        {
-            if (!string.IsNullOrEmpty(request.ExternalServiceCodeLegacy) && request.ExternalServiceEditionCodeLegacy is not null && request.ExternalServiceEditionCodeLegacy != 0)
-            {
-                await resourceRepository.UpdateExternalServiceCodeLegacy(resource.Id, request.ExternalServiceCodeLegacy, cancellationToken);
-                await resourceRepository.UpdateExternalServiceEditionCodeLegacy(resource.Id, request.ExternalServiceEditionCodeLegacy, cancellationToken);
-            } 
-            else
-            {
-                throw new ArgumentException("ExternalServiceCodeLegacy and ExternalServiceEditionCodeLegacy must be set when UseManifestFileShim is true");
-            }
-
-        }
         return Task.CompletedTask;
     }