Custom Action doesn´t work

Hi,

I created a custom action to set an email field to lowercase, like this:

Future<String> lowercase(String cString) async {
  // set string to lowercase while typing
  String result = cString.toLowerCase();
  return result;
}

Then I set up it on action flow on 'On Change' section, so I expected that when I type every character in Uppercase it goes to lowercase, but it doesn´t.

What I´m doing wrong?