index.php

<?php
// You need to have reference transactions enabled
// to enable it on sandbox account, you need to ask it here: https://www.x.com/thread/38753
// To enable reference transactions on live site you need to contact PayPal Business Services Group

require_once "lib/PaypalRecurringPayments.php";

$gateway = new PaypalGateway();
$gateway->apiUsername = "YOUR API USERNAME HERE";
$gateway->apiPassword = "YOUR API PASSWORD HERE";
$gateway->apiSignature = "YOUR API SIGNATURE HERE";
$gateway->testMode = true;

// Return (success) and cancel url setup
$gateway->returnUrl = "http://test.site/?action=success";
$gateway->cancelUrl = "http://test.site/?action=cancel";

$recurring = new PaypalRecurringPayments($gateway);

switch ($_GET['action']) {
    case "": // Index page, here you should be redirected to Paypal
        $resultData = array();
        $isOk = $recurring->obtainBillingAgreement("Test subscription", "testuser@gmail.com", 'USD', $resultData);
        if (!$isOk) {
            print_r($resultData);
        }
        break;
    
    case "success": // Paypal says everything's fine (see $gateway->returnUrl)
        $resultData = array();
        $details = $recurring->getBillingDetails($resultData);
        if (!$details) {
            echo "Something went wrong\n";
            print_r($resultData);
            return;
        }
        $billingAgreementId = $recurring->doInitialPayment($details->token, $details->payerId, 12.34, $resultData);
        if (!$billingAgreementId) {
            echo "Something went wrong\n";
            print_r($resultData);
            return;
        }
        echo "agreementId = ".$billingAgreementId;
        break;
    
    // Type ?action=test in browser to perform a subscription (reference) transaction
    case "test":
        $resultData = array();
        $billingAgreementId = 'B-5YW327438T794174S';
        // To perform payments you need to store billing agreement ID in your database
        $isOk = $recurring->doSubscriptionPayment($billingAgreementId, 21.17, $resultData);
        if ($isOk) {
            echo "Success!";
        } else {
            print_r($resultData);
        }
        break;
    
    case "cancel": // User cancel subscription process (see $gateway->cancelUrl)
        echo "User canceled";
        break;
}

?>