PayPal PayLater Payment Module Integration with osCommerce
Note: This manual is for osCommerce v4.
If the PayPal PayLater (another name for it is PayPal Express API v2) module is not set up yet set it up by clicking on Modules, Payment and Online tabs and then either click on PayPal quick setup button or click on Install button next to the required module (the other modules are available for setting up by switching on Show not installed and Show Inactive switches).
If you click on PayPal quick setup button choose the last option in the pop up window by clicking on the corresponding radio button.
Fill in the required information as it is shown on the screenshots below.
In order to get PayPal API Client ID and PayPal API Client secret as it is shown on the screenshot of the Details section above login to your Paypal developer account, click on My Apps & Credentials tab and then either create an app by clicking on the corresponding button or click on the required link of the existing app.
Copy and paste the Client ID and Secret into your Details section.
Note: Make sure you choose the required API Credentials (either sandbox like per the screenshot below or live).
Also the required Seller Merchant Id and Seller E-Mail Address can be found on your PayPal account. After you login to your PayPal account, in the Account settings section click on Business information tab to get your Seller Merchant Id.