Paystack is not involved in converting the currency of an international customer to Naira. The customer's bank determines the exchange rate and they deduct the Naira equivalent of whatever currency is in their bank account. However, we can guarantee that you will receive the exact amount you charged for in Naira, minus our transaction fees.
If your business is enabled to accept payments in US Dollars, the customer's bank will also handle the exchange rate and deduct the USD equivalent of their customer's currency. You can expect to get settled the exact amount you charged in US Dollars, minus our transaction charges.