LLER MÁS:

1) Click on ‘Checkout with PayPal’ button and see the experience.
2) If you get any Firewall warning, add rule to the Firewall to allow incoming connections for your application.
3) Checkout with PayPal using a buyer sandbox account provided on this page. And you're done!
4) The sample code uses default sandbox credentials which are set in config.php. You can create your own credentials by creating PayPal Seller and Buyer accounts on Sandbox here.
5) Make following changes in config.php:
- If using your own Sandbox seller account, update PP_USER_SANDBOX, PP_PASSWORD_SANDBOX and PP_SIGNATURE_SANDBOX values with your sandbox credentials
- SANDBOX_FLAG: Kept true for working with Sandbox, it will be false for live.
6) For trying out Mobile-EC, change the user-agent of your browser by installing a user agent switcher plugin and see how your website will appear on mobile devices.

Instructions to integrate 'Checkout with PayPal' on your website

1) Copy the files and folders under 'Checkout' package to the same location where you have your shopping cart page.
2) Copy the below <form> .. </form> to your shopping cart page.

<form action="paypal_ec_redirect.php" method="POST">
           <input type="hidden" name="PAYMENTREQUEST_0_AMT" value="10.00"></input>
           <input type="hidden" name="currencyCodeType" value="USD"></input>
           <input type="hidden" name="paymentType" value="Sale"></input>
           <!--Pass additional input parameters based on your shopping cart. For complete list of all the
               parameters click here -->
           <input type="image" src="https://www.paypalobjects.com/webstatic/en_US/i/buttons/checkout-logo-large.png"
           alt="Check out with PayPal"></input>
           </form>

3) Open your browser and navigate to your Shopping cart page. Click on 'Proceed to Checkout' button and complete the flow.
4) Read more details on Express Checkout API here