Generating Paypal keys
Note: This manual is for osCommerce v4.
Login to your Paypal account (https://www.paypal.com), direct your mouse to Account icon and then click on Account Settings option.
In the Account settings section, click on Business information tab to get your Seller Merchant Id.
Login to your Paypal developer account (https://developer.paypal.com), click on My Apps & Credentials tab, choose between sandbox or live mode 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 administration area.