/errors/experiment_error.proto

--- v18/errors/experiment_error.proto   2025-08-05 14:36:12.000000000 +0000
+++ v19/errors/experiment_error.proto   2025-08-05 14:36:14.000000000 +0000
@@ -132,5 +132,9 @@

     // Experiment length cannot be longer than max length.
     INVALID_DURATION_FOR_AN_EXPERIMENT = 30;
+
+    // The experiment's campaigns must self-declare whether they contain
+    // political advertising that targets the European Union.
+    MISSING_EU_POLITICAL_ADVERTISING_SELF_DECLARATION = 31;
   }
 }