[o_nate]

I guess the moral of this story is, if you're about to get on the bus, make sure you have enough battery left on your phone to last until you reach your destination. I use my phone to pay for a bus ticket every day, but I only have to show it when I get on. If I only had 1% left on the battery, I'd probably buy a paper ticket before heading to the gate though, just to be safe.

[Tsiklon]

In London the buses are entirely cashless, Contactless (Card or Apple Pay) or Oyster (Transport for London operated cashless ticketing system) only, no paper tickets are accepted.

On the tube one can purchase paper tickets, though these are somewhat rare now and cannot be purchased at all stations.