Interestingly, in the London, UK at least, demonstrating that you made an effort to pay a parking ticket but were not able to will normally mean you do not have to pay the fine.

For instance, I was fined for not displaying a parking ticket. But I took a picture of the machine that wasn't able to process my payment. I emailed picture to the appeals process and was forgiven the fine. Which essentially meant I got to park for free (shiny sticker)