You are dealing with a shyster company in the IPC and so don't imagine for a moment you are dealing with anything but intellectually malnourished scammers.
That NtK fails PoFA 9(2)(e)(i) in that there is no invitation to the keeper to pay the charge and therefore only the driver can be liable. You can appeal as the keeper mentioning that fact but don't hold your hopes up that they will even consider it. It would be for a judge to determine that point.
Signage is always a good appeal point. What was the reason for parking there? Is it a residential location? If so, what does the lease of the person you were visiting say about parking? What it doesn't say about parking is equally important.
