As it says, you have to file a defence within 14+5 days from the date on the form, so by 26 May. If you file an Acknowledgement of Service by this day, you have until 8 June to file your defence.
Of course you don’t need to pay anyone, but the claim will be on the basis that the driver of the vehicle entered into a contract by parking, and posting any other documents here will help your case.
Sitting in a car in a parking space in a car park is parking by any reasonable definition. So the purchase of the ticket and its duration will both be relevant.