+1. You inadvertently sent us and the CEO off in the wrong direction.
They issued a PCN because of what they knew i.e. a car parked on DYL with a BB displayed alongside a clock set at a time which, if correct, meant that the 3-hour exemption had lapsed = parked in a restricted street and a PCN.
You, and now us but not the council -yet, know that you were delivering items to the charity shop. Delivering is an exemption if criteria are satisfied, the main two being:
Was it necessary to transport the load in a vehicle, and
Was the vehicle where it was parked for no longer than necessary.
If you present to the council exactly what you've posted here then they would be justified in rejecting your claim to the delivering exemption because what immediately preceded the issuing of the PCN and what you were doing during the CEO's period of observation appears to be related to the sandwich shop, not the act of delivering.
Your story therefore needs to be rejigged IMO.
I parked because I was delivering items to *****, and here's my proof*;
I hold a BB and although I didn't need to display this because as I understood it delivering is an exemption from the restriction(particularly for me because carrying anything for more than a few feet is a challenge) I did display it because if a CEO appeared then I might not be at the car and as they wouldn't be able to see an exempt activity taking place they might issue a PCN and then I'd need to write to you explaining that I was delivering.
The plan was good, it was only the execution which let me down because I made a hash of things by simply opening my clock which was showing 6pm from the day before when it was last used.
Then the CEO arrived.
I hope that I've set the record straight, that you will accept that I was delivering and cancel the PCN.
Don't use this word-for-word but I suggest you include the relevant parts i.e. the reason you were parked; what you were doing; your belts and braces approach to conveying that you were authorised to park there; your mistake etc.
*- is the charity shop's note or whatever dated and timed? I hope it's the former only.