Doesn't matter. POPLA is unlikely to uphold an appeal either. However, a POPLA decision is not binding on the appellant.
Should your POPLA appeal be unsuccessful, then you will not be paying a penny to ECP if you follow the advice. Whilst there are probably good reasons for the drivers mistake in not realising the time limit on EV charging as ECP signs are not very good, this will still most likely go to a court claim down the line.
The modus operandi is well known to us and I can guarantee that as long as the claim is defenced, it will eventually be discontinued if not struck out first. They are hoping you are low-hanging fruit on the gullible tree who will pay up out of ignorance and fear.
For now, you can search the forum for recent POPLA appeals to get a feel for how they are structured and what points to put in them. When you have something, post it here and we will advise on whether it is suitable or needs any refinement before you send it. You have 33 days from the date of the appeal rejection to submit the POPLA appeal.
So, no rush and don't pin your hopes on POPLA. No one pays ECP if they follow the advice.