hint for mapping request payload error messages

Author: dbu

controller.rst

@@ -502,6 +502,14 @@ payload formats::
         // ...
     }
 
+.. tip::
+
+    If you write a json API, make sure to declare your route to use the json
+    format. This will make the error handling output a json response in case of
+    validation errors, rather than an HTML page.
+    
+    ``#[Route('/dashboard', name: 'dashboard', format: 'json')]
+
 Make sure to install `phpstan/phpdoc-parser`_ and `phpdocumentor/type-resolver`_
 if you want to map a nested array of specific DTOs::