Hello Alan,
Good to see your response. I haven’t done the Tube Challenge yet what with Christmas, strikes etc but I definitely plan to try to do it at some point this year. I’m very much looking forward to it. The resolution to my original query remains as in my last post above but I haven’t tried to purchase the Travelcard for real. As far as I know you purchase as you say – using the app then the purchase onto the smart card (which I have) using your phone.
Whilst it all seems possible it is mighty strange that only one company seems to offer the day Travelcard so until I, or someone else on here actually completes a successful purchase we can’t be certain that this is the way to go. I hope it is!