PayPal

On Payment Plugins management screen, click on os_paypal payment plugin to edit it. The following parameters need to be configured:

Basic

1. Environment: Set to Sandbox if you are testing the system and set it to Live when you go live. Please note that if you use Sandbox, you will need to register for a sandbox PayPal account (you could not use your real Paypal account in Test Mode)
2. Paypal Email: Enter the Paypal Email associated with your Paypal account.

Advanced

If you have a business PayPal account, you can follow the instructions at https://developer.paypal.com/api/rest/#link-getclientidandclientsecret , get Client ID, Client Secret of from PayPal account, enter it into os_paypal payment plugin parameters (Advanced tab) to allow admin to refund for a payment record from administrator area of the site