Multiplayer and IAP (probably noob question)

Hello! I’m doing an android game with multiplayer, using the low level API. Everything is going smoothly, I’m using JSON to communicate between the Server and the Clients and everything seems pretty safe to me since it’s all server sided.

But now I’ve ran into a problem. How can I make IAP safe? Is there a way I can make the purchase processing server side too? Because so far all the client does is tell the server what’s pressed and then receive data accordingly.

Anyone willing to explain me how can I make secure IAP with Unity 5.3?

Basically all I want to know is how to make IAP safe. Ecryption? Acess transactions directly in a server? Any hints?

Bump?