As of Release 3.0E, you can define a billing plan at header level valid for all items that are assigned to it.
In this step, you assign a billing plan type to a sales document type. This assignment is necessary if you want to use a header billing plan for a specific sales document type.
All document items with the same billing plan type (controlled
in the item category) are assigned to the header billing plan. To
display this assignment, mark the Header billing
plan field in the item billing plan. This can be
reversed manually if you want to define your own billing plans for
specific items. After reversing this assignment, you can maintain
the item billing plan separately.
An item which has been partially billed can be detached from the header but no long attached.
Assign a billing plan type to the sales document types for which you want to use a header billing plan.