 <p>PayPal is actually better than most in terms of enabling you to do testing. There's a complete testing sandbox solution (<a href="https://developer.paypal.com/webapps/developer/docs/classic/lifecycle/ug_sandbox/" rel="nofollow">support document</a>), and when adding/editing your REST API application, you can click the "Edit" link next to "App Redirect URLs" and specify both a testing URL and live URL for production. That should give you everything you need to test locally without exposing your site to the outside world.</p> <p>If it does end up giving you fits over using localhost, there's always services like <a href="http://readme.localtest.me" rel="nofollow">localtest.me</a>, that can let you get around it.</p>