/errors/recommendation_error.proto 

--- v15/errors/recommendation_error.proto   2024-02-20 20:29:00.000000000 +0000
+++ v16/errors/recommendation_error.proto   2024-02-20 20:29:02.000000000 +0000
@@ -88,5 +88,15 @@

     // The target multiplier specified is invalid.
     INVALID_MULTIPLIER = 18;
+
+    // The passed in advertising_channel_type is not supported.
+    ADVERTISING_CHANNEL_TYPE_GENERATE_NOT_SUPPORTED = 19;
+
+    // The passed in recommendation_type is not supported.
+    RECOMMENDATION_TYPE_GENERATE_NOT_SUPPORTED = 20;
+
+    // One or more recommendation_types need to be passed into the generate
+    // recommendations request.
+    RECOMMENDATION_TYPES_CANNOT_BE_EMPTY = 21;
   }
 }