How to add iOS capability: In-app-Purchase in UE4 environment?

I’m developing an iOS app with In-app-Purchase using UE4, I’ve made a mobileprovision with In-app-Purchase, also added this :
[OnlineSubsystemIOS.Store]
bSupportsInAppPurchasing=true
to iosEngine.ini, and I didn’t find any other settings item to add In-app-Purchase.
When I opened the xcode project on Mac , I found the capability: In-app-Purchase was missed, so I have to add it manually. So I want to know: how should I make In-app-Purchase work in UE4 directly? Thanks a lot!