Free Traffic Legal Advice

My issue in brief.
I parked in a private car park associated with an attraction.
I paid by ring go, made a mistake by one digit on the ringo codes.
The car park I paid was 100 yards away and run by the same operator charging the same fees.
They pcn'd me and rejected my appeal as have popla. In short it's up to the motorist to comply in full.

So now I pay, or I guess wait to be taken to court.

It seems to me a fair person would take into account: -
My intention to pay, that I actually paid, I paid the company who owned the carpark, albeit against a wrong reference number.

In that context a fine of £100 is unreasonable.

Firm now asking for their £100 or threatening debt collection.

Any views on what to do next and my chances, obviously do not want to face more legal costs

Thanks