How is it possible for my billing amount and the price quoted by the EVA Mobile system to differ?

Our mobile reservation system uses the SITA CCA authorization system to obtain an approval code. For that to happen, an on-the-spot currency conversion is made to US dollars. Some banks may send an instant message to customers immediately to notify them that this is taking place. However, the actual exchange rate that applies to the payment is calculated when the purchase confirmation is complete. Thus, there may be a minor difference in the indicated prices due to moment-to-moment foreign exchange fluctuations.