/errors/ad_group_error.proto 

--- v25/errors/ad_group_error.proto 2026-10-09 20:57:59.000000000 +0000
+++ v26/errors/ad_group_error.proto 2026-10-09 20:58:07.000000000 +0000
@@ -117,5 +117,9 @@
     // a campaign under Travel Ads in Search Campaigns.
     VERTICAL_ADS_FORMAT_SETTING_NOT_SUPPORTED_FOR_CAMPAIGNS_WITHOUT_ENABLED_TRAVEL_FEED =
         25;
+
+    // Demand Gen campaigns require EU political advertising self-declaration
+    // if any ad group targets the EU.
+    MISSING_EU_POLITICAL_ADVERTISING_SELF_DECLARATION = 26;
   }
 }