The following text was what I sent on the initial challenge:
Parking was paid for via the Ringo App, unfortunately I did not have my glasses with me and I selected what I thought was my car, which is down as a Silver Volkswagen in the Ringo App, however I had forgotten that I had added my fathers car into the app to help him pay for his parking as he is too old to use the app, and I selected his car, also a Silver Volkswagen by mistake. Once the confirmation text came through I realised the wrong vehicle had been selected and I tried to change the car via the app but the app only allows you to do this within the first 15 minutes and it was already 20 minutes later. I ran back to the car but the ticket had already been issued. Looking into the legalities of this point it would appear that it is a common issue and one that has been dealt with by multiple parking adjudicators. As the council has suffered no loss, as the time for parking the car was paid for, there should be no reason why the fine cannot be cancelled. The attached receipt proves that payment was made and as such no material loss has been suffered by the council. Furthermore, the signage is somewhat lacking in detail in this areas, as there are no terms and conditions shown, either for the parking area or the use of the app. As such we hope you will agree that payment for the period in question (see attachement) was indeed made in good faith, no material loss has been suffered by the council and that this PCN can be cancelled.