Problem with Unity IAP plugin and Windows Store (0x80190190)

We are updating one of our existing apps. We are attempting to implement IAPs through the UnityPurchasing plugin. However, we are experiencing errors when we attempt to purchase an IAP.

The way the UnityPurchasing plugin works, we call InitiatePurchase, and wait for an asynchronous callback from the Windows Store telling us whether the purchase succeeded or failed, and the reason why. Every time we attempt to purchase an IAP, the Windows Store tells us that the purchase failed because the user cancelled.

What the user sees when they attempt to purchase the app is first a sign-in prompt for the Windows Store. Once the user signs in, a prompt shows up that says "Try that again. Something happened on our end. Waiting a bit might help. The error code is 0x80190190, in case you need it." After the user closes this popup, then our app receives the callback that says that the purchase failed because the user cancelled.

The IAPs, once purchased, show up in the library of the purchasing accounts, suggesting that the transactions are being completed, but that we're not receiving confirmation properly from the Windows Store.

Has anyone had any similar issues with the Unity IAP plugin and Windows Store?

Thanks!