RingGo “no return rule” incorrectly applied

I paid for an hour’s parking at Catlings car park in Chesham today at 9:14, and needed to extend my parking by 30 minutes - I checked shortly after my paid time had elapsed. There is nothing on the sign that states a no return rule is in place. RingGo would not allow me to extend my parking, and so I had to risk a parking ticket as I could not return to my car before my paid time elapsed. I did not get a ticket, but this no-return issue has occurred before - I am not aware of any no-return rule in place at Catlings and have previously been able to top up parking with cash before the switch to RingGo/credit card only. I did not have a credit card on me today, so was reliant on RingGo (besides which, I couldn’t return to my car in time anyway). Please could you either point me to where this no-return rule is stated in the car park (it is not on the main sign or at the pedestrian exit), or update the machine ASAP to allow the same vehicle to pay again, ie ‘return’. Incidentally, the RingGo app is still stating I can’t pay to park there now at 6pm, many many hours later, when in fact it is now free to park without charge. Many thanks! Isobel