Please read
https://www.ftla.uk/private-parking-tickets/read-this-first-private-parking-charges-forum-guide/ and post anything you can with redactions as advised.
You should send a Subject Access Request to the parking company (not Moorside Legal) to obtain all the information they hold on you, which will include the original notice.
As a matter of urgency.
You have 14+5 days from the date on the N1SDT form to file a defence or Acknowledgement of Service. If you file an AoS you get an additional 14 days. You want to obtain the original notice before then.
It’s not a
fine, it’s an invoice for payment under the contract the driver entered into by reading the signs and parking. Is your car’s V5C correct? As long as the original notice was sent to the V5C address in time, you could be liable as registered keeper for the liability of the driver, but we need to see the original notice to know this.
Having gone to the expense of engaging Moorside Legal they won’t accept less to settle this.