Solution : https://service.sap.com/sap/support/notes/426120 (SAP Service marketplace login required)
Key words : 
transfer structure bapi selection owner apo, bapi transfer structure selection data apo, additional key words bop, apo backorder processing, bop_xvbep structure, cbop_xvbep structure, scheduled data, short text, prerequisites solution, transaction se11
Related Notes : 
       
| 426119 | Backorder processing: Syntax error BOP_XVBEP | 
| 426039 | Backorder processing: Syntax error VBX_S_DATA, VBX_S_HEAD | 
| 403602 | Backorder processing: MBDAT is in the past | 
| 400662 | Backorder processing: Configuration characteristics | 
| 375193 | Backorder processing: Composite SAP note on posting |