This looks straightforward, here's a draft representation:
Dear London Borough of Bexley,
I challenge liability for this penalty because the alleged contravention did not occur. Having reviewed the CEO's photos it is clear that there are two distinct bays separated by bay divider markings, however it is obvious that I missed these because a silver Honda was parked directly on top of those markings, please see the CEO's fourth photo.
While I appreciate it is not the council's fault that the silver Honda was parked on top of the road markings, that is not my fault either. As the bay divider markings were not visible, I had no way of knowing that my car was not parked in the pay and display bay. I attach a copy of my ringo receipt showing that I paid £14.80 to park.
Furthermore my car was parked in close proximity to the pay and display machine, while the permit only sign was away from my car and I walked in the opposite direction to the sign when I got out of my car, I am attaching a photo to illustrate the point.
In light of the above the PCN should be cancelled.
Yours faithfully,
Send this via the council website and keep a screenshot of the confirmation page.