Paypal Refund a Transaction API and Sample PHP Code. Let’s create a class with PayPal Username, Password, Signature ,API end point and Version. private $API_Username, $API_Password, $Signature, $API_Endpoint, $version; And with in the class it will be like this. class KvPayPalRefund { private $API_Username, $API_Password, $Signature, $API_Endpoint, $version; } Here we have sandbox Credentials and Live Credentials. So let’s create a constructor to make it ...