Billing rules are filter criteria that specify the conditions that sales records must meet to be part of the set of sales of a Billing Scenario. For example "Opportunity Stage equals Closed/Won" is a billing rule that sets apart the closed deals from all opportunities in your organization.
All invoicing with invoices is always done in the context of a Billing Scenario. So at the time of billing, you pick one of your pre-defined scenarios and the application automatically filters the sales for that scenario in the bulk billing mode, or a single sale in the single invoice mode.
invoices provides three types of billing rules: Opportunity, Opportunity Line Item, and Revenue Schedule billing rules. These types differ on the object to which the field on the filter criteria applies. For each type, you can use the standard and custom fields for that object, and its parent objects up to three levels. So for example, "Account Type equals Reseller" is an Opportunity type billing rule.
The Opportunity Line Item and Revenue Schedule type of billing rules also specify the conditions that the opportunity products must meet to be included in an invoice, in addition to specify the conditions the sales records must meet to be part of a Billing Scenario. An example is "Schedule Date greater than 11/1/2011" and "Schedule Date less than 11/31/2011" for sales with products that have a scheduled revenue. The rules in the example constrain the invoices for November 2011 to include the installments or subscription for that month only. So the billing rules provide the means to setup the billing process for products with one-time payments, as well as products with recurrent payments such as products sold in installments or subscription type of products.
You add one or more Billing Rules to a Billing Scenario to define the sales for that scenario, and to constrain which products are included in the invoices for these sales.
Select the billing rule field. Add the selected field to the billing rules panel to create a billing rule. Pick the billing rule operator and assign a value to the selected billing rule field, or tick the variable checkbox. A variable billing rules means that its value is assigned at the time of billing Save the the billing rules.