[Closed] Reasons for OnInitializeFailed: PurchasingUnavailable for PlayMarket?

Hello everyone,

I have an app, published in PlayMarket and used Unity IAP.

In most cases everything is ok, but sometimes users can't buy my products due to OnInitializeFailed: PurchasingUnavailable error.
They wrote me that internet connection is on and purchases are enabled in device/playmarket settings.

So question is - which another reasons may cause PurchasingUnavailable error?

I want to fix it ASAP cause I get a bunch of negative reviews everyday from users who can't unlock more levels in my app, but I can't find a reason for it. As I said before, everything is ok for 95% of my users.