fix: max-affected preference not failing for rpc with strict handling

docs/references/api/preferences.rst

@@ -292,3 +292,7 @@ With :ref:`RPC <functions>`, the preference is honored completely on the basis o
       "details": "The query affects 14 rows",
       "hint": null
   }
+
+.. note::
+
+  It is important for functions to return ``SETOF`` or ``TABLE`` when called with ``max-affected`` preference. A violation of this would cause a :ref:`PGRST128 <pgrst128>` error.

docs/references/errors.rst

@@ -267,6 +267,10 @@ Related to the HTTP request elements.
 |               |             | implemented.                                                |
 | PGRST127      |             |                                                             |
 +---------------+-------------+-------------------------------------------------------------+
+| .. _pgrst128: | 400         | ``max-affected`` preference is violated with ``RPC`` call.  |
+|               |             | See :ref:`prefer_max_affected`.                             |
+| PGRST128      |             |                                                             |
++---------------+-------------+-------------------------------------------------------------+
 
 
 .. _pgrst2**: