Show the Notice to Keeper (NtK) you received. They have no idea of the drivers identity and unless their NtK fully complies with all the requirements of PoFA, they cannot hold the Keeper liable. If the NtK does not state a "period of parking", or even it if does but it is less than 5 minutes, the NtK is not PoFA compliant.
Unfortunately, the vat majority of people that receive these PCNs have no idea of their rights and how to properly challenge them. If you're here receiving advice and following it, you will not be paying penny.