Monetizing VR games / VR in-app purchases?

Hey guys, 
we're wondering why there's no payment system for in-app purchases directly from within VR. 
What's the biggest challenge for monetizing in-app VR content as a VR dev? What are your thoughts on this? 
Survey on VR payment 
Takes only 2 minutes. 6 simple multiple-choice questions. We hate long surveys, too 😅

Cheers,
Richard from Holoswitch / triple A code