如何在paypal php rest api沙盒模式下退还销售金额

<?php

require 'vendor/autoload.php'; // 引入 PayPal 的 PHP SDK

use PayPal\Rest\ApiContext;
use PayPal\Auth\OAuthTokenCredential;
use PayPal\Api\Amount;
use PayPal\Api\Refund;
use PayPal\Api\Sale;
use PayPal\Api\RefundRequest;

$clientId = 'YOUR_SANDBOX_CLIENT_ID';
$clientSecret = 'YOUR_SANDBOX_CLIENT_SECRET';

$apiContext = new ApiContext(
    new OAuthTokenCredential($clientId, $clientSecret)
);

$apiContext->setConfig([
    'mode' => 'sandbox', // 设置为沙盒模式
]);

$saleId = 'SALE_ID_TO_REFUND';
$refundAmount = '10.00'; // 退款金额

$refundRequest = new RefundRequest();
$refundRequest->setAmount(new Amount(['total' => $refundAmount, 'currency' => 'USD']));

$sale = new Sale();
$sale->setId($saleId);

$refund = $sale->refund($refundRequest, $apiContext);

if ($refund->getState() == 'completed') {
    echo '退款成功！';
} else {
    echo '退款失败！';
}