Solution : https://service.sap.com/sap/support/notes/1048627 (SAP Service marketplace login required)
Key words :
system issued error message f6 804 ', symptom service charge settlement, account assignment element 'fund'', simulate service charge settlement, execute current occupancy principle, account assignment element 'fund', advance payment transfer posting, ps cd/fi ca, object transfer posting, object transfer postingprerequisite