It's an informal challenge so no need to go into a deep dive.
One other thing - did you miss seeing the sign when you parked? I presume so and you can add that the sign wasn't seen when parking as it was attached to a parking sign half buried in vegetation. I would also include you are a resident and have a parking permit.
I would say:
The contravention of 'Parked wholly or partly in a suspended bay or space- permit holder only electric vehicle charging bay'
alleged on the PCN did not occur for these reasons.
1. The permit bay is not an electric vehicle charging bay.
2. The contravention code is 21a - a is a suffix that means temporary traffic order. I could not see any such order at the location.
3. My car was outside no 199 and at most trivially adjacent to no 197, which is the extent of the suspended part of the bay.
I look forward to your early confirmation of cancellation of this PCN.
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I'm not sure what to say about point 2 - someone else may chip but I think it's not a correct use of the regulations.
I also wondered if they are turning the bay into EV charging - I can see reference to Goldhurst Terrace in this but not at this location:
https://www.camden.gov.uk/documents/d/guest/introduction-of-electric-vehicle-recharging-point-parking-places-proposals-dated-27-february-2025