Custom Field Validation V3

Hey, I′m still trying to make my custom field validation, this time in Ninjaforms 3.

I′ve found this snippet:

add_filters( ‘ninja_forms_pre_validate_field_settings’, ‘my_ninja_forms_pre_validate_field_settings’ );
function my_ninja_forms_pre_validate_field_settings( $field_settings ) {
return $field_settings;
}

Not very helpful I must say.
I can get the entered value here and validate it, but how can I add an error message and make the submission fail?!

Thanks