If it becomes standard for public parking to be signed, everyone would know. If payment QR codes in general start being signed, your payment app might even know. Lastly there could even be signage by the code to help novices.
It wouldn’t need a separate app if, for instance, a standard QR payment format way created. If you just want a link to a website to pay, then naturally that would be less secure, but you could always put the URL below the QR code for redundancy (QR would only save time typing then).
If it becomes standard for public parking to be signed, everyone would know. If payment QR codes in general start being signed, your payment app might even know. Lastly there could even be signage by the code to help novices.
The point of a code is to not have an app in the first place. Thus there’s no way to validate it.
It wouldn’t need a separate app if, for instance, a standard QR payment format way created. If you just want a link to a website to pay, then naturally that would be less secure, but you could always put the URL below the QR code for redundancy (QR would only save time typing then).