Reading your first post, it seems to me that you knew you should not have parked there, but decided to chance your arm and park, hoping a CEO didn't come along and find your car. Is that a correct summation ? There is no mandatory observation period before a PCN may be served where a vehicle is seen in an apparent parking contravention.
Although this forum is here to assist PCN recipients and also bring councils to account for their various tricks they use to game the system, sometimes a PCN really is correctly served, and this seems to be one of those times. Others have hinted that you might be able to claim loading, (the food), but if you had just parked to pick up a takeaway, then I think this argument would fail. The other thing is that the council are almost certain to reject any representations you submit, so to get a final and unbiased judgment, you'd have to take them to London Tribunals. This means the full PCN penalty would be in play; no discount if you lose.
Of course there may be a 'technical' appeal, totally unrelated to the actual contravention that could win at London Tribunals. These are based on council mismanagement of the enforcement process. Councils must obey the regulations that govern their enforcement same as you, and if they don't, it is a procedural impropriety and grounds for cancellation of the PCN. However, nobody has yet suggested anything.
Of course, recommendation is not to pay yet, so you should at least submit some representations stating why you parked there, (the food) and claim you were loading pre-ordered goods. Was the food such that it needed to be collected and taken somewhere quickly, so meant you could not park some distance away ? If this was so, put it in your reps. Post up their response here when you get it. Provided your reps are received by them before the discount period expires, they will re-offer the discount.