Everything is in the title.
Including VoiceInterface.h in your project won’t compile without including OnlineSubsystem.h first.
It fails at the line declaring a delegate:
This is because I’ve violated the “include what you use” rule and not included OnlineDelegateMacros.h in that header file. If you would try adding that (or leaving OnlineSubsystem.h) as a workaround that would be appreciated.
I’ll make the changes and get it out in a new version of the engine.