Hi,
Everyone knows that we are working in a world of third and fourth generation technologies. So whenever in time of down time we can frankly inform the same to our customers and they will understand it. But if their issue is really important try to do it internally as you will always have a backup option or do it offline and take customer consent for that, otherwise offer them a call back and try to contact them when the system is ready so that they will feel like we really took care of their issue
