Copying here for when pepipoo goes offline:
Dear Transport for London,
I challenge liability on the basis of a procedural impropriety, specifically it is unlawful for you to serve a postal PCN in these circumstances. I refer you to the red route panel decision in Commercial Plant Services Ltd & others v Transport for London (2230060716, 25 May 2023) published at www.londontribunals.gov.uk/sites/default/files/keycases/Red%20Route%20Panel%20Decision.pdf
It follows that the PCN must be cancelled.
Yours faithfully,