cf7

add_filter('wpcf7_posted_data', 'my_wpcf7_posted_data');
function my_wpcf7_posted_data($posted_data) {
    if ( isset( $posted_data['subjects'] ) ) {
		$form_url = get_permalink( 3166 ); // page with form
        $posted_data['next_form_url'] = $form_url . '?' . http_build_query( array( 'subjects' => $posted_data['subjects'] ) );
    }
    return $posted_data;
}