Solution : https://service.sap.com/sap/support/notes/336589 (SAP Service marketplace login required)
Key words :
key field bapi_te_po_items-po_item, account assignment table ekkn, purchase order tables, general bapi guidelines, user-defined fields, header table ekko, customer include ci_ekkodb, customer include ci_ekpodb, customer include ci_cobl, respective customer enhancement
Related Notes :
| 867018 | Customer fields transfer to the back end |
| 445169 | BAPI_PO_GET_DETAIL: Integrated customer enhancements |
| 395311 | BAPI_PO_CREATE: Customer enhancements not copied |
| 390742 | Customer enhancements not transferred |