Kindly be informed that in order to trigger ATU from carpark exit / ERP gantry, it will require to meet the following conditions:　

1. Carpark exit must be full EPS and ATU enabled by LTA, not all carparks are. You can tell it is EPS when you enter the carpark, there will be a signage.　

2. Flashpay card must be in your car IU.

3. There is no ATU triggered within the past 3 days　

4. When the card balance is insufficient for the transaction that you are attempting to pay for.

一般来说，2和4肯定满足的。我遇到的应该是第一点，那个carpark可能没有AUT enabled。关于第三点，大部分人应该不会遇到，但是6楼朋友说的情况可能就正好遇到。解决办法是不要每次只充20，可以充多点。