Solution : https://service.sap.com/sap/support/notes/493027 (SAP Service marketplace login required)
Key words : 
flat-rate installation, terms individual simulation, additional selection field, periodic billing, transaction easibi, thesame day, function enhancement, initial screen, interval check, billing order
Related Notes : 
       
| 636529 | EASIBI: Reading interval check cannot be suppressed |