How does postal etc query the balance?

If the postal ETC is a charge card, then the postal bank savings card is bound. The debit card itself has no money. When using ETC, the deduction information will be sent to the Postal Savings Bank, which will deduct the money from the savings card. There is no money in the ETC card, so the balance cannot be queried. ETC credit card (credit card) can check the balance through WeChat, mobile APP and online banking.