Hospital car parks are not usually covered by bylaws but are private land, and therefore PoFA 2012 can be used for parking on the land.
The notice, however, may well not comply with the requirements of PoFA 2012 to transfer liability.
The IAS will not uphold any appeal.
This will go to a court claim, in all likelihood, which you will be able to defend with a good defence with advice here, and ultimately the claim will be discontinued.
Since you were at a hospital, did you ask PALS to cancel the charge for you?