In message , Martin Petrov
writes

I know it's probably the wrong attitude, but is it actually worth the
time and effort to recoup a couple of quid? Presumably, that's not your
only journey on the day, and by the end of the day, you're likely to hit
your daily cap, making that particular error not worth wasting your time
on?

Depends what the actual problem was. If it was failure to register a
touch out, then the maximum cash fare is applied for the journey and
this amount doesn't count towards the daily cap.
--
Paul Terry