What is the best course of action to appeal the PCN.None!
Why?
Because the PCN as such is history - issued 2 Sept.- and a Notice to Owner for the full penalty has already been issued: informal reps against the initial PCN can only be made until a NTO is issued.
https://walthamocm.itsvc.co.uk/PCN/MainDisplayAre you the vehicle's registered keeper? If so, why have you not mentioned the NTO?
If you are the keeper but have not received the NTO then you cannot appeal this further(this right falls to the 'recipient' of a NTO) all you can do procedurally is wait for the next notices - charge certificate and Order for Recovery- and then file a witness statement. It's routine but a bit of a palava.
If you are not the registered keeper then who is? Only they may make formal representations.
Bring us up to speed on who's who pl, not the contravention because we're not at this point.