我正在尝试调用 ExpressCheckout 并执行即时更新 API，但无论我做什么，它似乎都会返回一个无效的运输总错误。我知道在实时运行时需要使用 SSL，但是我正在尝试针对沙箱进行测试，但仍然遇到这些错误。
我的简单 HTML 测试页面：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Express Checkout with Callback API - PayPal</title>
</head>
<body>
<h1 align="center"> Express Checkout with Callback API </h1>
<h3 align="center"> PayPal </h3>
<form method=post action=https://api-3t.sandbox.paypal.com/nvp>
<input type=hidden name=USER value=xxxxxxxxxxx>
<input type=hidden name=PWD value=xxxxxxxx>
<input type=hidden name=SIGNATURE value=xxxxxxxxxxxxxxxxxxxxxxx>
<input type=hidden name=VERSION value=63.0>
<input type=hidden name=PAYMENTREQUEST_0_PAYMENTACTION value=Sale>
<input name=PAYMENTREQUEST_0_AMT value=19.95>
<input type=hidden name=RETURNURL value=https://www.YourReturnURL.com>
<input type=hidden name=CANCELURL value=https://www.YourCancelURL.com>
<input type=hidden name=MAXAMT value=100.00>
<input type=hidden name=callback value=....../callback.php>
<input type=hidden name= callbacktimeout value=5>
<input type=hidden name= l_shippingoptionisdefault0 value=true>
<input type=hidden name= l_shippingoptionname0 value=Ground>
<input type=hidden name= l_shippingoptionlabel0 value=5 Days>
<input type=hidden name= l_shippingoptionamount0 value=10.00>
<input type=hidden name= shippingamt value=10.00>
<input type=submit name=METHOD value=SetExpressCheckout>
</form>
</body>
</html>
我的 callback.php 脚本托管在我的服务器上：
<?php
foreach ($_POST as $key => $value) {
$value = urlencode(stripslashes($value));
$req = "&$key=$value";
}
//Build string
$method = $_POST['METHOD'];
$version = $_POST['CALLBACKVERSION'];
$token = $_POST['TOKEN'];
$currencycode = $_POST['CURRENCYCODE'];
$localecode = $_POST['LOCALECODE'];
$street = $_POST['SHIPTOSTREET'];
$street2 = $_POST['SHIPTOSTREET2'];
$city = $_POST['SHIPTOCITY'];
$state = $_POST['SHIPTOSTATE'];
$country = $_POST['SHIPTOCOUNTRY'];
$zip = $_POST['SHIPTOZIP'];
//If PayPal acocunt has US address
if ($country=="US") {
echo "METHOD=CallbackResponse&L_SHIPPINGOPTIONNAME0=Ground&L_SHIPPINGOPTIONLABEL0=5 to 7 Days&L_SHIPPINGOPTIONAMOUNT0=10.00&L_SHIPPINGOPTIONISDEFAULT0=true";
}
//If PayPal account has a non-US address
else {
echo "METHOD=CallbackResponse&L_SHIPPINGOPTIONNAME0=Next Day Air&L_SHIPPINGOPTIONLABEL0=7 to 14 Days&L_SHIPPINGOPTIONAMOUNT0=20.00&L_SHIPPINGOPTIONISDEFAULT0=true";
}
?>
我已从代码中删除了一些敏感信息，并将所有运费值更改了 100 次，如果有一些愚蠢的错误，请见谅。任何帮助将不胜感激，谢谢！