```
--- v25/errors/mutate_error.proto   2026-07-21 22:09:38.000000000 +0000
+++ v26/errors/mutate_error.proto   2026-11-09 16:22:49.000000000 +0000
@@ -1,72 +1,76 @@
 // Copyright 2026 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.

 syntax = "proto3";

-package google.ads.googleads.v25.errors;
+package google.ads.googleads.v26.errors;

-option csharp_namespace = "Google.Ads.GoogleAds.V25.Errors";
-option go_package = "google.golang.org/genproto/googleapis/ads/googleads/v25/errors;errors";
+option csharp_namespace = "Google.Ads.GoogleAds.V26.Errors";
+option go_package = "google.golang.org/genproto/googleapis/ads/googleads/v26/errors;errors";
 option java_multiple_files = true;
 option java_outer_classname = "MutateErrorProto";
-option java_package = "com.google.ads.googleads.v25.errors";
+option java_package = "com.google.ads.googleads.v26.errors";
 option objc_class_prefix = "GAA";
-option php_namespace = "Google\\Ads\\GoogleAds\\V25\\Errors";
-option ruby_package = "Google::Ads::GoogleAds::V25::Errors";
+option php_namespace = "Google\\Ads\\GoogleAds\\V26\\Errors";
+option ruby_package = "Google::Ads::GoogleAds::V26::Errors";

 // Proto file describing mutate errors.

 // Container for enum describing possible mutate errors.
 message MutateErrorEnum {
   // Enum describing possible mutate errors.
   enum MutateError {
     // Enum unspecified.
     UNSPECIFIED = 0;

     // The received error code is not known in this version.
     UNKNOWN = 1;

     // Requested resource was not found.
     RESOURCE_NOT_FOUND = 3;

     // Cannot mutate the same resource twice in one request.
     ID_EXISTS_IN_MULTIPLE_MUTATES = 7;

     // The field's contents don't match another field that represents the same
     // data.
     INCONSISTENT_FIELD_VALUES = 8;

     // Mutates are not allowed for the requested resource.
     MUTATE_NOT_ALLOWED = 9;

     // The resource isn't in Google Ads. It belongs to another ads system.
     RESOURCE_NOT_IN_GOOGLE_ADS = 10;

     // The resource being created already exists.
     RESOURCE_ALREADY_EXISTS = 11;

     // This resource cannot be used with "validate_only".
     RESOURCE_DOES_NOT_SUPPORT_VALIDATE_ONLY = 12;

     // This operation cannot be used with "partial_failure".
     OPERATION_DOES_NOT_SUPPORT_PARTIAL_FAILURE = 16;

     // Attempt to write to read-only fields.
     RESOURCE_READ_ONLY = 13;

     // Mutates are generally not allowed if the customer contains non-exempt
     // campaigns without the EU political advertising declaration.
     EU_POLITICAL_ADVERTISING_DECLARATION_REQUIRED = 17;
+
+    // The combination of resources in this mutate is not supported for
+    // multi-party approval.
+    MULTI_PARTY_APPROVAL_UNSUPPORTED_RESOURCE_COMBINATION = 18;
   }
 }
```