Failed to start IAP error on LaunchCheckoutFlow()

[STARasGAMES]

Unity 2017.4.1f1 (specified in Supported Unity Versions
Platform SDK 1.24.0 (latest)

Call:

IAP.LaunchCheckoutFlow(sku).OnComplete(LaunchCheckoutFlowCallback);

In LaunchCheckoutFlowCallback I got Message<Purchase> with IsError=true
Full error data: 
Code: 1 
HttpCode: -1 
Message: 'OVR77152342: Failed to start IAP: OVR60915022 (1971005)'

sku 100% correct
Test-user payment method specified (Always succeeds - 4111 1177 1155 2927, Exp.month: 10, Exp.year:20, CVV2: 111, Country: United Kingdom)
Organization payment method specified
Initialization done
Entitlement check done
IAP.GetProductsBySKU(SKUS); - works correct and returns expected values

What I'm doing wrong?  😞

[STARasGAMES]

@imperativity

Yes, I have Oculus runtime installed. 
Entitlement check works, and I can access test-user information.
Also IAP.GetProductsBySKU(SKUS); - works correct and returns expected values

[STARasGAMES]

@imperativity
It's an offline problem, because when I disable internet access right before calling LaunchCheckoutFlow() it still returns the same error as before.