Scam, have you heard of this one.

Yes, I read about this earlier this week, and mentioned it to my DH (not that he will have taken any notice!), because, unlike most of these scans, I think this is a very easy one to fall for.
You arrive at a car park, realise that the machine doesn't take cash or card and you need to download an app - so you're already a bit flustered. Who is going to check that a sticker hasn't been placed over the reputable app on the machine? It's OK saying go to a reputable site, but these car parks all use different apps, so until you arrive, you don't know which one you will need!