Paypal NVP身份验证失败

当前使用PHP+cURL在xampp上测试NVP SetExpressCheckout Paypal功能（沙箱模式），无论我做什么，我都会收到以下错误：

错误代码10002:身份验证/授权失败。您没有进行此API调用的权限。

$nvp = array(
    'METHOD' => 'SetExpressCheckout',
    'VERSION' => '98',
    'USER' => $user,
    'PWD' => $pwd,
    'SIGNATURE' => $signature,
    'RETURNURL' => $returnurl,
    'CANCELURL' => $cancelurl,
    'PAYMENTREQUEST_0_PAYMENTACTION' => 'Sale',
    'PAYMENTREQUEST_0_AMT' => '20.00',
    'PAYMENTREQUEST_0_CURRENCYCODE' => $currency,
    'REQCONFIRMSHIPPING' => '0',
    'NOSHIPPING' => '1',
    'ALLOWNOTE' => '0',
    'LOCALECODE' => 'US'
    'L_PAYMENTREQUEST_0_NAME0' = 'A product name';
    'L_PAYMENTREQUEST_0_AMT0' = '20.00';
    'L_PAYMENTREQUEST_0_QTY0' = '1';
    'L_PAYMENTREQUEST_0_ITEMCATEGORY0' = 'Digital';
);
$request = 'https://api-3t.sandbox.paypal.com/nvp?' . http_build_query($nvp);
$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, $request);
curl_setopt($curl, CURLOPT_VERBOSE, true);
curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
$response = urldecode(curl_exec($curl));
curl_close($curl);

奇怪的是，如果我在浏览器中键入curl request（与$request变量相同），我会从端点获得SUCCESS和令牌，我不知道这是和卷曲本身有关，还是其他原因，我试着完全禁用我的防火墙，但错误仍然存在。。。