add_filter( 'wpf_redirect_url', 'pp_migration_orientation', 10, 2 );

function pp_migration_orientation( $redirect, $post_id ) {

    // if being redirected to the orientation page, append e-mail address to the end of the URL to prepopulate the ActiveCampaign form

    if ( $redirect == "/website-migration" ) {

        $current_user = wp_get_current_user();

        $user_email = $current_user->user_email;

        return '/website-migration?email='.$user_email;

    } else {
        return $redirect;
    }

}