Change Action URL

Hello,
I am getting nuts with changing the action URL.

I put this in the “Aditional Settings field”

add_filter( 'wpcf7_form_action_url', 'wpcf7_custom_form_action_url' );

In my functions.php I use this code…but nothing happens 🙁

function wpcf7_custom_form_action_url($url)
{
global $wpcf7_contact_form;
if ( $wpcf7_contact_form->ID === 33564 ) {
//its the payments page
// stop email being sent
$wpcf7->skip_mail = 1;
return 'http://denis-online.de/sml/nl.php';
} else {
return $url;
}
}
add_filter( 'wpcf7_form_action_url', 'wpcf7_custom_form_action_url' );

What is the solution? Or is there another extra Plugin.

Thanks & Cheers,
Denis