Do the Sequence Diagram for the following use case: For execute purchase, the game triggers the action When the action happens, you need some sort of item id to see what item the user is buying. Purchaseltem(id) Send that info to the server Validation happens against the server It returns an error code Error code 0 -> success Anything else -> fails If it succeeds, the Module grants rewards If not, Shows an error message IAP Module Execute purchase Game Server > Payment validation