Transactions in a currency other than the card currency are processed by the Visa within 2–3 days. The transaction is carried out in two stages: funds are first held (preauthorization) and then debited. In this case, the debit is made at the current exchange rate, not at the rate on the date of the initial hold. If the exchange rate changes while the transaction is processing, the debited amount will be different from the amount originally held. Depending on the exchange rate fluctuations, the amount of the final withdrawal may be greater than the initial blocking, which can cause a negative balance on the card (more funds were actually debited than were on the card at the time of the transaction).
We neither charge penalties for a negative balance nor block your card. Just add the required amount of funds to the card as soon as you can.