Nobody pays (not so) Smart Parking. I didn't see the NtK that's been removed but SP do not usually rely on PoFA to hold the keeper liable. Once you have shown your NtK, suitably reacted but showing all dates, we can confirm.
If the NtK is not PoFA compliant then it is a doddle to get cancelled. (not so) Smart Parking have no idea who the driver is unless you contacted them and told them it was you (bad move). They have sent you the NtK because you are the registered keeper. There is no obligation in law for the keeper to identify the driver.
Because (not so) Smart Parking do not rely on PoFA, liability for the PCN cannot be transferred to the keeper. AN appeal from the keeper stating that there is no liability usually gets it cancelled. If not, a POPLA appeal will put it to an end.
Just remember, no "I parked...". It should always be "The driver parked...".