One frosty morning I arrived at my local station to find that the ticket machine was broken. No matter, I thought, I have got a smartphone, and I hurriedly set about buying my ticket that way.
This was not as easy as I had hoped, fiddling between credit card and phone with freezing cold fingers, but, by the time I got on the intercity to Geneva I had an e-ticket and I proudly showed it to the conductor.
Unfortunately she was less than impressed and told me in no uncertain terms that my ticket was not valid. Why, only became clear several weeks later when a letter arrived from Swiss railways euphemistically named "revenue protection service".
The good people there tell me the formal payment for my ticket from my credit card company arrived four minutes after my train left the station. That means, they say, that I bought my ticket on the train - and that is not allowed.