Solution : https://service.sap.com/sap/support/notes/512561 (SAP Service marketplace login required)
Key words :
enjoysap transactions fb60, similar fi transaction, tax tab page, tax base amount, terms tax base, changed item amounts, purchase order items, purchase order, account items, line items
Related Notes :
| 719340 | MIRO FB60 FB70 - tax base cannot be changed |