Solution : https://service.sap.com/sap/support/notes/317514 (SAP Service marketplace login required)
Key words :
'modified fields' choose 'change' enter, additional key words sfac, transaction sfaw module pool, select 'cust' = 'x' confirm, add field caufvd-func_area, missing modifiable fields, afvgd-func_areawbs elements, functional area field, customer field selection, customers field selection
Related Notes :
| 325444 | Functional area in the network not ready for input |
| 85799 | Collective note: Cost of sales accounting problems |