[xxs]

Indeed, it could be a common issues. Some places transposition systems even allow use of bank cards as 'ticket'

[dgxyz]

Yeah I'm in London so that's what we use here. But a lot of the European transport systems just chuck it through as a single transaction so if you buy three tickets it looks like repeated attempts to transact and is blocked.

Athens is another one that got me last year.

[xxs]

Funny - both London and Athens were in my mind when I wrote the comment.