At the moment the volume of people logging on to notify they don't need to do a tax return is huuuuuuge! By 9am on Monday there were already several thousand people who had updated online. And it just keeps getting more. If you have business to do like estimate, check payment etc, the app is handling the traffic very well but you can't do the non lodgement advice on the app

Living. You can lodge the lump sum claim any time now. As long as it is lodged by June 30 next year. You don't have to have done your taxes first. However you do need to lodge your taxes by June 30 or you won't get the payment s (you used to have two years to do it all, you now only have one!)