Handling External Payment Flow for a Free App in Microsoft Partner Center

When we add a product for Windows in Partner Center, we must also add pricing and availability, including a pricing detail. Currently, we have set it to $0. However, when a user downloads the app, they must create an account through the web and complete a $99 payment there. Microsoft has raised a concern that the app is indirectly redirecting users to payment. How can we resolve this issue while keeping our payment process web-based?