Well I wouldn't put too much effort into it, they'll reject it regardless - entirely expected and not a setback in the least.
Something like:
I have your invoice. I am the keeper of the vehicle and I dispute your "parking charge". I deny any liability or contractual agreement.
As your Notice to Keeper (NTK) does not fully comply with ALL the requirements of POFA 2012, you are unable to hold the keeper of the vehicle liable for the charge.
Besides, other shortfalls, as an example, your NTK fails Paragraph 9(2)(e)(i) of Schedule 4 of the Protection of Freedoms Act 2012 insofar as it must explicitly invite the keeper to pay the unpaid parking charges. The wording must clearly convey this invitation, and mere implication or indirect suggestions are insufficient.
Partial or even substantial compliance is not sufficient. There will be no admission as to who was driving and no inference or assumptions can be drawn. You have relied on contract law allegations of breach against the driver only.
The registered keeper cannot be presumed or inferred to have been the driver, nor pursued under some twisted interpretation of the law of agency. Your NTK can only hold the driver liable.
There are two options available you now - either cancel the invoice or provide me with a POPLA code.
With measured indifference,