deductEvent method to reduce the outstanding, unbilled balance of Eventsfor an AutoBill, by creating a new Event, with a negative value. Use the reverseEvent call to remove a specific, previously recorded Event.
Note: Calling deductEvent will fail if it results in a negative Rated Unit balance on the AutoBillItem. Subscribe does not support negative balances on Rated Units.
Use reverseEvent to credit an Account for previously billed Events.

