We've added fixed amount discount codes. 

A fixed amount discount applies a discount to the entire order, not per item.  For example, if the fixed amount is $100 then the customer gets $100 off the order no matter how many items the customer purchases. It is not $100 per item, it's $100 per order.

This feature requires advanced ecommerce to be available and enabled on your account.

You can find these settings in your account under Commerce -> Discount codes