Optional cash back amount to return to the customer.
This amount is to be presented with an implied decimal point. For example, US $10.00 must be represented as 1000, and $0.10 is likewise simply 10. The largest possible CashBack amount is "99999", yielding a maximum US dollar amount of $999.99. This field may not contain a negative number.
For cash back transactions, the TransactionAmount must contain the sum total of the purchase amount PLUS the CashBack amount. If the purchase is for $10 and the customer requests $20 cash back, CashBack should be set to "2000" and TransactionAmount must contain "3000".
Note that only US currency is supported for debit transactions.