Which API Should I Use?
The quick answer: it depends on your goals, your platform and what kind of goods or services you're selling. The Instant Buy APIs are for selling physical goods, while digital goods sellers should use Google Play In-app Billing for Android for native Android apps. To engage your customers with offers and loyalty programs, use the Wallet Objects API.
For selling physical goods or services
Instant Buy for Android — If you exclusively sell physical goods, you can integrate Google Wallet Instant Buy with your Android app free of charge. With Instant Buy, you keep your existing payment processor and leverage Google Wallet to optimize your payment flow to boost sales.
Instant Buy for web — To sell physical goods on web apps and mobile apps that run on browsers, use Instant Buy for web. You'll keep your existing payment processor and optimize your payment flow with Google Wallet, just like with Android.
For selling digital goods
Google Play In-app Billing for Android — Any app published through Google Play can implement In-app Billing to sell digital content. In addition to your Google Play Developer Console account, all you need is a Google Wallet merchant account. See the Android documentation for full detail on this API.
For engaging with your customers
Wallet Objects API — This API provides a platform to connect your business to millions of Google users and showcase your loyalty programs, offers, and more. You can engage with your customers through Google's always-available platform with location-based notifications, real-time updates, and messaging.