Solution : https://service.sap.com/sap/support/notes/380675 (SAP Service marketplace login required)
Key words : 
additional key words faz, compulsory condition pr00, solution implement notes 174608, user exit pricing_copy, user exit achieves, attached source code, source code, payment items, billing document, vf 073 message
Related Notes : 
       
| 381348 | Using user exit, customer exit, VOFM in SD | 
| 351391 | Incorrect condition values for down payment items | 
| 179789 | Control PRICING_COPY | 
| 174608 | Statistical conditions in down payment items (1) | 
| 170183 | |
| 113347 | Down payment process. as of Release 4.0x (standard) |