"We asked our user to pay X at T but when we received the payment at T' the price wasn't the same so we need to match the price currently so ask for X' actually

"We asked our user to pay X at T but when we received the payment at T' the price wasn't the same so we need to match the price currently so ask for X' actually and when we receive the payment at T'' the price has changed so actually ask them for X'' oh but wait..."