Gratuity amount for settling restaurant industry transactions.
This field contains the gratuity (tip) amount of the transaction being settled. This amount is only sent when the PTechCharge component's IndustryType is set to "itRestaurant". If a transaction includes a GratuityAmount amount, the SettlementAmount must reflect the total of the original Authorized Amount plus the GratuityAmount.
This must be formatted as a dollar amount with a real decimal point, excluding the dollar sign. For instance "12.00".