Solution : https://service.sap.com/sap/support/notes/626451 (SAP Service marketplace login required)
Key words : 
payment clearing item reason, final billing document, payment clearing, billing document, final invoice, item level, order item, billing plan, payment process, payment print
Related Notes : 
       
| 652786 | SAPscript: Down payment information is generally printed | 
| 638658 | SAPscript down payment print: VAT in final amount | 
| 626665 | Smart Forms: Invoice print with down payments | 
| 586442 | Down payment request number not available for print | 
| 569318 | Enhancement of billing document printout: Down payments (4) | 
| 555279 | Enhancement of billing document printout: Down payments (3) | 
| 532052 | Values for down payments missing in billing docmnt printout | 
| 523803 | Enhancement of billing doc print: Down payments (2) | 
| 304408 | Enhancement of billing document printout: Down payments (1) | 
| 113347 | Down payment process. as of Release 4.0x (standard) |