To display the Paypal payment method on the front end. You must have the PayPal Account. While creating the PayPal Account you will get the Client ID. You can use that client ID into the ‘BookUpp – Paypal Payment Gateway Addon‘.
To Create a PayPal Account. Go through the following PayPal Documentation.
Documentation Link : https://developer.paypal.com/tools/sandbox/accounts/#create-a-personal-sandbox-account