What the Keeper has been sent is a fake penalty notice. It is a fraudulent attempt to gain money without lawful reason. In other words, it is a criminal act that APCOA are undertaking.
There is a whole essay on this elsewhere on this forum that I have explained. Any attempt to recover a supposed penalty issued under byelaws, can only be challenged in the magistrates court after information has been laid and a summons issued.
APCOA will try to recover the "penalty" into their own coffers, whereas, if the penalty were challenged in court and the challenge was unsuccessful, any fine imposed would go to the public purse, not APCOA's back account. However, APCOA are offering an appeal and secondary appeal route through POPLA, which is not the platform for challenging "penalty" purportedly issued under statutory belaws.
You can read up on the reasoning here:
Why APCOA have no authority to issue Penalty Notices under railway bylawsYou should also read this thread, whilst it applies to SABA rather than APCOA, it is fully relevant to this and any other "penalty" issued by an unregulated private parking firm:
Saba Parking Services - Railway parking site - debt collector before initial notice?So, I advise that you follow the advice given in that second link about SABA and you make contact with the police, not the useless Action Fraud, and report APCOA for fraud by false representation (Fraud Act 2006, s.2),
Contact your MP, report APCOA to the DVLA and your local police force economic crime unit, as per the examples in the thread linked above.
You will never pay a penny to this firm that operates outside of the law.