Solution : https://service.sap.com/sap/support/notes/193993 (SAP Service marketplace login required)
Key words :
--> billing quantity indicator tvcpf-fkmgk, additional key words vf01, billing quantity indicator, vas additional data, afs item overview, source code lines, system displays items, data field zero_item, level pricing data, line item number
Related Notes :
| 208121 | TABLE_INVALID_INDEX in AFS billing document |