Can I use Unity IAP with Facebook Gmeroom but without "lite payments"?

Hi
I'm using:
Unity 2017.4.11.f1
Unity IAP v.1.21
Platform: Facebook Gameroom (native windows)
Facebook SDK: 7.13.0 (embedded)

In the Unity IAP manual it is mentioned that I have to use Payments Lite, but I have a client-server game, so I have game server where I would like to verify my in-app purchases (it works for all the other platforms that my game runs on).
When I try to use the Unity IAP without Payments Lite, I seem to have an issue with OnInitialized handler never get called, and so - StoreController is not available. I would be completely happy without having a product list, but not without a store controller.

So the questions is: how can I safely use the non-lite payments with Unity IAP? Or can I use some sort of a mix: for example having a configured lite products for the Unity IAP to be happy and still using my server for purchases validation? Or the only choice for me - is to make my own implementation of the Store for Facebook (just to live safely without a product list request)?

 

Thanks for the fast reply, Jeff!

crying a river...