Free Traffic Legal Advice

I have recieved a notice to owner from Devon County Council on 20.08.25 for when my car was parked on a road side at 11:41am on 13.07.25. The person parking the car there paid for a ticket at around 12.40 (evidence of this can be provided via the app they used) I understand the payment was late due to poor signal and the purchase not going through in first attempt. The driver on returning to the car did not have any yellow ticket on the car and it says a PCN was serviced on 13.07.25 but there is no evidence of this and certainly nothing on the car window. Not sure what I should now do? The fine is saying it is £50 and will rise to £75 if not paid within 28 days.