Can a waived parking fine still have an admin fee?

Our work car parking is looked after by a private company. I recently received a fine for not paying - it turns out I'd misentered my car rego by one digit. I had paid, so sent through proof of payment BEFORE the payment due date.

Below is the email I received (after the payment due date for the original fine);

Our appeals team have assessed it and their comments are below

"Hi there, this certainly looks like an honest mistake so thanks for taking the time to send us the details. We do still charge a $15 fee for user error/incorrect registrations/incorrect app which covers our costs such as issuance, infringement correspondence and the processing of the dispute.

This is purely discretionary and given your clean history with us we are more than happy to exercise this discretion here. I have discounted this in the system which is at wegetdebt.co.nz/breach

Are they allowed to add a fine while waiving the ticket?