It really stinks when you’ve been saving up your Google Opinion Rewards money, but you’re just a few cents short of buying something. Google has not thus far allowed you to apply that credit and pay the difference, but it looks like that’s changing. We’ve gotten multiple tips from readers who have been offered just that option in the Play Store.
The current official behavior when you don’t have enough in Google Play balance to cover a purchase is to force you to use a card, PayPal, or carrier billing.
Play Store Has Started Allowing Split Payments Between Google Play Credit And Another Payment Method was written by the awesome team at Android Police.
Source: Andriod Police