I assume ParkingEye did not enclose any other documents alongside their PCN, such as a copy of your lease agreement?
So, you are the hirer and not the registered keeper. This means you have no liability, as they are not seeking to hold you liable as the hirer.
Appeal online
as the hirer only with the below:
Dear Sirs,
I have received your Parking Charge Notice (Ref: ________) for vehicle registration mark ____ ___, in which you allege that the driver has incurred a parking charge. I note from your correspondence that you are not seeking to hold me liable as the hirer of the vehicle, under Schedule 4 of the Protection of Freedoms Act 2012 ("The Act").
There is no obligation for me to name the driver and I will not be doing so. I am therefore unable to help you further with this matter, and look forward to your confirmation that the charge has been cancelled. If you choose to decline this appeal, you must issue a POPLA code.
Yours,
If appealing online, be careful there are no drop down/tick boxes that cause you to identify who was driving, and keep a close eye on your spam folder for their response. If they do not respond within 28 days, chase them.