acf backend error handling

I want to add custom error handling in acf backend. Here’s my code:

function dfg_acf_validate_value( $valid, $value, $field, $input_name ) {

    // Bail early if value is already invalid.
    if( $valid !== true ) {
        return $valid;
    }

    if( $value != '30' and $value != 360 ) {
        return __( 'Please choose a valid type!' );
    }
    return $valid;
}

add_filter('acf/validate_value/name=dfg_service_type', 'dfg_acf_validate_value', 10, 4);

and in the backend when I choose something else (instead of 30 or 360) nothing happens. What’s the reason for that?

I actually found that the hook is not fired. What’s the reason for that?

function dfg_acf_validate_value( $valid, $value, $field, $input_name ) {
    
        if( $value != '30' ) {
            wp_mail('test@example.com', 'subject', 'message');
        }
        return $valid;
    }
    
    add_filter('acf/validate_value/name=dfg_service_type', 'dfg_acf_validate_value', 10, 4);