diff --git a/billing/v1/billing.proto b/billing/v1/billing.proto
index f40d05b8..c18875bf 100644
--- a/billing/v1/billing.proto
+++ b/billing/v1/billing.proto
@@ -2098,6 +2098,9 @@ message ListInvoiceRequest {
  
   // OPTIONAL: vendor (aws, azure, gcp)
   string vendor = 2;
+
+  // Optional. If set, return only child invoices for this billing group.
+  string billingInternalId = 3;
 }
 
 // Response message for the ListInvoice rpc.
diff --git a/openapiv2/apidocs.swagger.json b/openapiv2/apidocs.swagger.json
index 344ca27c..6d7c2634 100644
--- a/openapiv2/apidocs.swagger.json
+++ b/openapiv2/apidocs.swagger.json
@@ -44019,6 +44019,10 @@
         "vendor": {
           "type": "string",
           "title": "OPTIONAL: vendor (aws, azure, gcp)"
+        },
+        "billingInternalId": {
+          "type": "string",
+          "description": "Optional. If set, return only child invoices for this billing group."
         }
       },
       "description": "Request message for the ListInvoice rpc."