Solution : https://service.sap.com/sap/support/notes/595772 (SAP Service marketplace login required)
Key words : 
'ipricingitemcommon' ipc api interface, ipc api describe, ipc user exits, ipc user exit, ipc pricing formulas, abap pricing api, amount formula reason, prc_pricing_api function group, sap software center, public hashtable getdynamicreturnvalues
Related Notes : 
       
| 672672 | Provision of additional subtotals for Internet Sales | 
| 625074 | Terms of payment determination on item level II | 
| 580235 | Terms of payment determination on item level | 
| 530835 | IPC Support Packages for CRM 3.0, CRM 3.1 and CRM 4.0 | 
| 486061 | How to get patches for CRM Internet Pricing Configurator |