Thanks for your reply! In terms of the process, the letter said that any further informal challenges won't be acknowledged so the next step is then for the Notice to Owner, so I need to wait for that I believe.
I'll have payments every weekday from 2018-2020, after that was Covid and when we were allowed back to the office, then it became hybrid working so I would do mostly two days a week, unless I got one of the limited spaces at the office. So it would look patchy after that on the basis that I'd be down to two days a week, and I can occasionally park at the office so even when I am in, there's not necessarily a payment for the car park. As it happens, the majority of the time I'm in, I will be in that car park and obviously have paid, but I think on that basis it wouldn't help much to show payments a couple of times a week as it could look to them that I only pay every so often (and also be the luckiest person on earth that until now I've avoided a ticket...!). They also won't be able to find anything on my reg at all, be it that car park or anywhere else. And I've lived in the area my whole life so there's a comprehensive history there!
I've got a screenshot of the attempted (as it turned out) payment on Apple pay at 8:37 and a screenshot from our work phone system of the calls made (time and length). I tried at 8:52 just in case they were open early (which coincidentally is the time they started observing me without a ticket), and then again spoke to the guy at 9:01 at which point I then went back to the car to buy a new ticket. And have the email back to him saying 'I got a ticket, what do I do?' which shows at least that I was very promptly back to my car, so should show I acted as quickly as was possible based on their timelines. And there's absolutely no part of the timeline they can point to where I acted in a way that would indicate I was trying to get away without paying - I had to wait until their office opened and then paid in full as soon as I could after that. I don't think there's anything I wish I did have in terms of actual evidence with times etc so I feel confident on that front.
What an adjudicator should see is that I have the screenshot with the time my phone/bank believed the payment was made (8:37), the times I then tried to call after and how quickly I was back at my car buying the full ticket after that once they'd confirmed what I should do. The signal is notoriously poor in Chichester which I mentioned in my email as the reason for there seeming to be two choices - go to the office and wait until 9 to use our phone system, or hang around and be an undetermined amount of time late for work while I waited for a parking attendant who may or may not show up during the day. So on that basis, I'm already surprised the first challenge failed given how clear it seems to me that I did everything I could to resolve asap, and they're not out of pocket. I still paid for the full day there and then, so the fine should then look like a ridiculous overreaction to uphold it. Their reply didn't really indicate they've read my email to be honest anyway. I did read that adjudicators also take into account what's a fair application of a fine and this definitely isn't.