[Paypal] paypal direct payment 直接使用信用卡付款

測試paypal direct payment api的筆記過程。

Website Payments Pro 解決方案

https://developer.paypal.com/docs/classic/products/website-payments-pro/

在Website Payments Pro這一包的產品下，裡面包含以下的整合技術

Direct Payment, Express Checkout, and additional PayPal solutions and tools — like Virtual Terminal, Fraud Management Filters, and reference transactions.

簡介Website Payments Pro
https://developer.paypal.com/docs/classic/paypal-payments-pro/integration-guide/WPWebsitePaymentsPro/