PayPal Express Checkout is a payment wallet gateway that allows you to accept PayPal transactions using a hosted page on PayPal Web site. 

This gateway supports the following features:

• Purchase using gateway hosted page
• Recurring payment

The following fields are required:

1. Username – Your API username and is different from your account username.
2. Password – Your API password and is different from your account password.
3. Signature

To obtain the API credentials, you need to have a personal or business account with PayPal. Follow the steps below to obtain your credentials.

1. Login to PayPal Web site and go to your Account Settings. 
2. Click on Update for the "API Access" section.
3. Under the "NVP/SOAP API integration" section, click on Manage API credentials.
4. Copy the API credentials (API Username, API Password and Signature) information.

For recurring payment, you will need to contact PayPal to enable "Reference Transactions" in your account first.

If you are using a URL rewriter, please ensure that it is not rewriting your checkout's page URL to lowercase as PayPal will redirect back to your site passing a security token that needs to be in mixed-case.