In WordPress admin panel, go to Smartpay > Settings. Select Payment Gateways Tab. In the General tab Under Payment Gateways, you will see by default PayPal Standard is selected.
Next, Select PayPal Standard Tab under Payment Gateways. Next, Put PayPal Email and Paypal Identity Token in the input box. Click on the Save Change button to save the settings.
Now you are ready to use PayPal as a payment gateway in WP Smartpay.