/errors/ad_group_ad_error.proto 

--- v22/errors/ad_group_ad_error.proto  2026-01-23 15:36:21.000000000 +0000
+++ v23/errors/ad_group_ad_error.proto  2026-01-23 15:36:26.000000000 +0000
@@ -72,5 +72,8 @@
     // An ad of this type is deprecated and cannot be updated. Only removals
     // are permitted.
     CANNOT_UPDATE_DEPRECATED_ADS = 12;
+
+    // Ad sharing is not allowed.
+    AD_SHARING_NOT_ALLOWED = 13;
   }
 }