If your web application's success depends on how quickly and easily users can make transactions, then PayPal is a solution you can't afford to overlook. This book helps you determine which PayPal option is best for your situation, and provides step-by-step instructions for implementing the payment method you choose—whether you're accepting money via the Web or mobile devices for products and services, donations, or anything else. You'll find sample code written primarily in PHP and Objective-C, as well as use cases for executing options with PayPal's API. By the end of this book, you'll have a clear understanding of PayPal and how you can get the most out of its powerful features, no matter how much API programming experience you have. Learn how to work with the PayPal API, and choose the right integration method for your project Explore PayPal’s Express Checkout option, including its unique workflow and four methods of operation Examine the Website Payment Pro method—with a focus on direct payments Consider Adaptive Payments and learn how to set permission levels for their use Use PayPal in your iOS or Android-based mobile app with the new Mobile Express Checkout method Test your PayPal implementation with the sandbox