Solution : https://service.sap.com/sap/support/notes/175958 (SAP Service marketplace login required)
Key words :
bapi parameter extensionin/extensionout save, schedule line data save, rfc-compatible function module, create function module sd_sls_incompletion_read, additional key words, english field names, english field names, attached source code, create structure bape_vbkd, include program lvbak001
Related Notes :
396596 | Export tables for SD_SALESDOCUMENT_CREATE |
390465 | BAPI SD: Document creation - texts and incompleteness |