Solution : https://service.sap.com/sap/support/notes/201895 (SAP Service marketplace login required)
Key words :
additional key words me21n, 6b support package 3, account assignment tab, account assignment category, account assignment categories, 'account assignment' tab, repeat account assignment, additional menu option, 'activate repeat' pushbutton, additional pushbutton
Related Notes :
| 315676 | ME21N: Multiple acct. assignment for existing items |