Why not a short URL where one can at least read the domain name and see if it looks reasonable before progressing with whatever the task ($£kr) is
The real solution is establishing a trusted channel - citizens need to know they should only pay for municipal parking through their city's official domain (e.g., sf.gov/parking). But this isn't possible when it's some random parking company. I don't see a great solution.
I'm convinced the only responsible solutions are chip-only payment processors and conventional coin machines, as pricey as they are.