This would be easy to win if it ever got in front of a judge. It never will, even if they initiate a claim.
For now, you can try an appeal which will be rejected but it will get you a POPLA code for a secondary appeal, which has a slightly better chance of being accepted. If it isn't, don't worry.
Nobody pays EPC if they're here getting advice. The most probable outcome will be that a county court claim will eventually be issued. As long as it is defended, any old defence will do, it will eventually be discontinued.
No need to overthink this. It is a well known modus operandi of ECP and their bulk litigator DCB Legal. For now, simply appeal as the keeper with the following to ECP:
I dispute your 'parking charge', as the keeper of the vehicle. I deny any liability or contractual agreement and I will be making a complaint about your predatory conduct to your client landowner.
As your Notice to Keeper (NtK) does not fully comply with ALL the requirements of PoFA 2012, namely no "invitation", or any synonym of the word, for the keeper to pay the charge as per paragraph 9(2)(e)(i), you are unable to hold the keeper of the vehicle liable for the charge. Partial or even substantial compliance is not sufficient. There will be no admission as to who was driving and no inference or assumptions can be drawn.
Since your PCN is a vague template, I require an explanation of the allegations and your evidence. You must include a close up actual photograph of the sign you contend was at the location on the material date as well as your images of the vehicle.
I suggest you cancel the PCN or issue me with a POPLA code.
It won't be successful but it will get you the rejection with a POPLA code.