The keeper should contact the hospital PALS service and request that they cancel it.
For reference, PoFA 9(2)(e)(i) is not complied with in that the NtK does not "invite the keeper to pay the unpaid parking charge". POPLA has upheld appeals on this basis in the recent past.
I think the choices you have are:
1. Try and get PALS to get it cancelled.
2. Appeal as the keeper and if rejected, appeal to POPLA using the kitchen sink and highlight the PoFA failure mentioned above.
3. Pay the charge.
4. Do nothing and wait and see if they issue a claim.