The fees and foreign exchange rates that apply to the transaction.
If the fees are in terms of the baseAmount (source account) currency, then the effective rate is equal to 1 - (fees * baseRate / baseAmount).
If the fees are in terms of the transferAmount (destination account) currency, then the effective rate is equal to baseRate - (fees / baseAmount).
In the preceding expressions, fees is equal to the sum of all feeAmount.currencyAmount values in the fees array.