Negative balance after a card payment

Card payments must be systematically authorized, meaning that the card will verify that the customer has enough money on the account set as the payment source at each payment attempt. 

In very specific cases, described below, the account balance may become negative after using card (physical, contactless mobile payment or virtual card).

Cases in which an account balance becomes negative

1. When a payment is made in a place with very poor or nonexistent internet connection, such as an airplane.
   It may take the airline’s internet network a longer amount of time to communicate information from a user’s application to the network. In the meanwhile, a customer might continue to spend money. When information regarding a transaction is finally communicated, the customer might not have a sufficient balance for the purchase. The delayed transaction will subsequently overdraft the account balance.
2. When the final amount charged to the card is superior to the amount authorized.
   This may happen, for example, when an individual takes the tube in London. When the customer passes her card at the tube entrance, a 1 £ authorization is debited. At the end of the trip, when the passenger pass card again to exit the underground, the trip finally costs a total of 5 £. The authorized transaction will be updated with the right amount and force the debit even if the balance is insufficient in order to allow the passenger to leave the underground. As a result this scenario could lead to overdraft.
   
   This could also happen during a trip abroad due to exchange rates. If the exchange rate rises between the moment a transaction is made and when it is confirmed (which may take several days), a different amount may be charged and create a negative account balance.
3. After several successive purchases, if a payment terminal hasn’t sent validation information for the transaction quickly enough.
   The payment will still be made to the merchant, but if there are any technical difficulties in the information sent between the payment terminal and card networks, the authorized transaction, and hence the debit, might be delayed by a few minutes. If the customer makes other purchases in the meantime, it is possible that the account balance might be insufficient once the delayed transaction is finally debited. As a result the account will become negative.
4. If a merchant takes a long time to send a positive (or negative) response regarding a transaction
   The authorized transaction can be automatically reversed after 10 days if the merchant did not confirm it. If the merchant finally rectifies the situation and asks for a new debit because the original transaction was reversed, then the account balance can turned negative. Especially if the customer spent the money that got reversed initially. Click here for more information.