Solution : https://service.sap.com/sap/support/notes/434526 (SAP Service marketplace login required)
Key words : 
partial delivery/milestone billing condition values, add optional import parameter itemtyp, additional key words shipment conditions, import/export parameter interface, milestone billing partial delivery, attached source code corrections, type     optional    pass valueitemtyp, calculation type 'fixed amount', delivery-related billing, milestone billing occurs
Related Notes : 
       
| 25144 | Freight conditions for milestone billing |