Making a Callbackproxy blueprint function

Hi

In my app I want to be able to save things on iCloud so I’m looking in to doing it with OnlineSub->GetSharedCloudInterface();. Which I understand a little bit. However I’m trying to make a function like “Make an In-App Purchase” which I have a base script but I don’t get the second function like In App purchases. Does anyone know if there are any tutorials of some sort or more information about using cloud on ue4? I haven’t found much

Thanks in advance