We would like to set up an Order level modifier that discounts 100% of the order net total after Lin

We would like to set up an Order level modifier that discounts 100% of the order net total after Line level modifiers have been applied.  Currently modifier is discounting the gross order total and receiving Error "The list price or the selling price is negative and the profile "ONT: Negative Pricing" is set to "N"".  Thank you