/errors/request_error.proto 

--- v15/errors/request_error.proto  2024-02-20 20:29:00.000000000 +0000
+++ v16/errors/request_error.proto  2024-02-20 20:29:02.000000000 +0000
@@ -64,6 +64,10 @@
     // Page size specified in user request is invalid.
     INVALID_PAGE_SIZE = 22;

+    // Setting the page size is not supported, and will be unavailable in a
+    // future version.
+    PAGE_SIZE_NOT_SUPPORTED = 40;
+
     // Required field is missing.
     REQUIRED_FIELD_MISSING = 9;