Originally Posted by
AllieKat
It happened to me in Cardiff, they told me that it was because I used an American Express and American Express crashes the self-service machines. It happened to @jamar in London with a non-Amex and he was told it was chip and signature that did it.
I doubt it was anything to do with it being American Express, my chip and pin Amex has never crashed them. She probably just noticed their were more amex signature cards than other cards.