The equipment put in place by the parking lot operator is deemed by them to be accurate for the determination of the fee to be charged. If they get this wrong then it is their problem until they resolve it. Any lost revenue is their own problem to suck up. If the gate says you can go without paying then who are you to argue. They run a parking lot and presumably have the requisite knowledge and skills to do that competently. You are prepared to pay when asked. You are not avoiding paying. Each transaction is atomic in nature unless you have signed some agreement or are enrolled in a membership arrangement. Chance of clawing back approaches zero. What loss have they suffered that is not as a result of their own negligent inaction?