Modify Multiple Bookings mode success message

/*
 * This snippet will modify Multiple Bookings mode success message
 */
function my_em_booking_success( $return, $EM_Multiple_Booking ){

 if ($return['result']) {
  $return['message'] = $return['message'].'<br><br>'.'Welcome to <a href="http://wp-events-plugin.com/">Events Manager</a>';
 }

 return $return;
}
add_filter('em_action_emp_checkout','my_em_booking_success',10,2);