You need to respond to the council in writing before the end of the period of 28 days of the service of the Notice to Owner. There is a section of the form which can be used to set out your response. At this point, copies of all evidence should also be sent in.
If the challenge is successful, the PCN is cancelled and you pay nothing. If the challenge is unsuccessful, you will be sent a Notice of Rejection (NOR) and a Notice of Appeal form (NOA) - a form to be filled out and submitted to the Traffic Penalty Tribunal. You must send this appeal form to the Traffic Penalty Tribunal before the end of the period of 28 days beginning with the date the Notice of Rejection is served (deemed to be 2 working days after posting).