The Xsolla PHP SDK by Xsolla integrates payments into applications. Resources include UI customization, client for API methods, and webhook server. Billing, monetization, and conversion are the services provided by Xsolla.
At TwilioCon in San Francisco today, Twilio is unveiling a new billing system for its API. This new in-app billing solution is called "Twilio Connect," and it provides a much simpler model for developers to implement customer billing when it comes to recurring charges for SMS and phone calls.
The W3C Web Payments Working Group has published working drafts of Web Payments HTTP Specifications that include the Web Payments HTTP API 1.0 and Web Payments HTTP Messages 1.0. The two specifications are designed to work together to enable payment requests outside of a browser context.