OK, so the PCN has been served within the 28 day period allowed, and the section for submitting reps seems OK.
Did you actually look at the sign for the bay where you parked, or did you just chance your arm ? The sign is clear enough - "Loading Only". No days or times means it is a 24x7 restriction.
At the moment I see no credible reps unless you can tell us more.
There may be a 'technical appeal' based on Brighton mismanagement of the enforcement process, but for Brighton I'm not sure of one, but hopefully somebody may suggest something.