The exchange rate is automatically converted by mconvert.net Currency Convertor API, but API convert just exchange rate. So you have a profit you need to fill this field with a number she will act as a percentage. For example: If you enter the number 2 would mean 2%, and if users exchanged 100 dollars to euro exchange rate is 1 USD = 0.97 EUR, will receive the 96EUR with the real exchange rate and if you set 2% your profit of 96 EUR will It was 1.92 EUR and the customer will receive 94.08 EUR. Enter number without %.
You can setup fixed or percentage fee. This fee will be used to calculate total amount for payment for client. For example: If user sell 100 and if fee is 10% must pay 110 or if user sell 50 and fee is fixed 5.99 must pay 55.99 and etc. If do not want to setup fee leave blank.