Milestone Billing

 Milestone billing means distributing the total amount to be billed
over multiple billing  dates in the billing plan.  
As each milestone is successfully reached, the customer is billed either
a percentage of  the entire project cost or simply a pre-defined amount.
During sales order processing, the system determines from the item category
whether a  billing plan is required and, if so, which type of plan 
The type of billing plan that is determined at this point is set
up in Customizing and  cannot be changed in the sales document. 
Billing plans for periodic billing and milestone billing plans for
project-related milestone  billing have different overview screens
so that you can enter data relevant to your  processing.  
For example, for milestone billing, you must be able to enter data to
identify the  individual milestones.

 IMG configuration :

1.  Maintain billing plan types for milestone billing in OVBO.
2.  Define date description in SM30 - V_TVTB.
3.  Maintain Date Category for Billing Plan Type IN OVBJ.
4.  Allocate date category in SM30 - V_TFPLA_TY. 
5.  Maintain date proposal for Billing Plan Type in OVBM.
6.  Assign Billing Plan Type to Sales Documents Type in OVBP.
7.  Assign Billing Plan Type to Item Categories in OVBR. 
8.  Define rules for determining the date in OVBS.