In which case, they have failed to comply with the requirements of Schedule 4 of the Protection of Freedoms Act to hold you liable as the hirer, despite what they claim on their notice. Here's an example of an appeal you can use as the hirer:
Dear Sirs,
I have received you Parking Charge Notice [(PCN number)] for Vehicle Registration Mark [VRM]. I am appealing as the vehicle's hirer. There is no obligation for me to name the driver at the time and I will not be doing so.
To hold me liable for the charge as the hirer of the vehicle, you must meet the conditions specified in Paragraph 14 of Schedule 4 of the Protection of Freedoms Act 2012 (“the Act”). I note from your correspondence that you have failed to meet these conditions. These failures include (but are not limited to) a failure to include the additional documents mentioned by 13(2) of the Act, as required by 14(2)(a).
As a result of this, you are unable to recover the specified charge from me, the hirer. As I do not have liability for this charge, I am unable to help you further with this matter. I therefore look forward to your confirmation that the Parking Charge Notice has been cancelled and that no further action will be taken against me. If you refuse to do this, you must supply me with a POPLA code.
Yours faithfully
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.