Testing in-app billing from Xamarin.Forms app

Hello,

I have setup an App in App Store as a free app. Not yet submitted.
I added an in-app purchase as auto-renewable subscription

Trying to implement/test this using https://github.com/jamesmontemagno/InAppBillingPlugin

This returns true- await billing.ConnectAsync(true);
This then breaks- var prodInfo = await billing.GetProductInfoAsync(ItemType.Subscription, prodIds);
UNKNOWN ERROR returned.

My only thought is that the prodId for the in-app purchase is not available (yet).

QUESTION:
Does the app have to have been submitted for the target in-app purchase to be exposed in the app store for testing with a sandbox appleId account?

Thanks