Welcome to FTLA.
Can you please show us the back of the notice?
The good news with Smart Parking is that they never comply with the requirements of Schedule 4 of the Protection of Freedoms Act (there's a link in my signature if you'd like to understand the legislation), which is the only mechanism that allows parking companies to hold registered keepers of vehicles liable. Without complying with that, they can only hold the driver liable - and unless you tell them who that is, they have no idea!
Once we've seen the back of the notice, and assuming you're the registered keeper of the vehicle (tell us if not!), the below can be sent as an appeal, and will almost certainly lead to the charge being cancelled:
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 registered keeper, under Schedule 4 of the Protection of Freedoms Act 2012 ("The Act"). You have chosen not to issue a Notice to Keeper in accordance with The Act, and it is now too late for you to do so.
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.
The template above has a 100% success rate with Smart so far.