PayPal Sandox 代码 400 返回空值

所以我在弄乱PayPal沙盒，但由于某种原因，它不想退回给我一个数组进行购买。相反，它只返回 null。 我可以使用 curl 通过 api 检索令牌，但处理测试卡仍然返回 null。以前有人遇到过这个问题吗？

<?php
    use PayPal'Api'Payer;
    use PayPal'Api'Details;
    use PayPal'Api'Amount;
    use PayPal'Api'Transaction;
    use PayPal'Api'Payment;
    use PayPal'Api'RedirectUrls;
    require 'src/start.php';
    $payer = new Payer();
    $details = new Details();
    $amount = new Amount();
    $transaction = new Transaction();
    $payment = new Payment();
    $redirectUrls = new RedirectUrls();
    //PAYER
    $payer->setPaymentMethod('paypal');
    //Details
    //acutal prices(20 dollars is a test)
    //Amount
    $amount->setCurrency('GBP')
      ->setTotal('22.00')
      ->setDetails($details);
    $details->setShipping('2.00')
    ->setTax('0.00')
    ->setSubtotal('20.00');
    //Transaction
    $transaction->setAmount($amount);
      // ->setDescription('Membership');
    //Payment
    $payment->setIntent('sale')
      ->setPayer($payer)
      ->setTransactions([$transaction]);
    //RedirectUrls
    $redirectUrls->setReturnUrl('http://localhost:8000/paypaletc/pay.php?approved=true');
      // ->setCancelUrl('http://localhost:8000/paypal/pay.php?approved=false');
    $payment->setRedirectUrls($RedirectUrls);

    try{
        $payment->create($api);

    } catch(PayPal'Exception'PayPalConnectionException $e){
      echo $e->getMessage();
      // header('Location: paypaletc/error.php');
    }
    var_dump($payment->getLinks());

我的开始.php：

<?php
    use PayPal'Rest'ApiContext;
    use PayPal'Auth'OAuthTokenCredential;
    // session_start();
    // $_SESSION['user_id'] = 1;
    // $db = newPDO('mysql:host=localhost;dbname-site', 'homestead', 'secret');
    // $user = $db->prepare("
    //   SELECT * FROM users
    //   WHERE id = :user_id
    //   ");
    // $user-execute(['user_id' => $_SESSION['user_id']]);
    // $user = $user->fetchObject();

    require __DIR__ . '/../vendor/autoload.php';
    // API CREDS
    $api = new ApiContext(
    new OAuthTokenCredential(
      "AfhmDCIi9Gc6cTuMv8Y4wVENTycXAkLfCWJ37v2uvQ0FJO7nqoL_JssmUaYAFBMtQD85xOfk1mHMtMb_",
      "EABb--WImsBgy3Ck_MmsVD-uVa--plWBwxqzaLFt33_DDRz7cV5GkNQbfB_ZH-1z1a9NU4ictM98erdJ"
      )
    );
    $api->setConfig([
    'mode' => 'sandbox',
    // 'http.ConnectionTimeOut'=> 30,
    // 'log.LogEnabled' => false,
    // 'log.FileName'=>'',
    // 'log.LogLevel'=>'FINE',
    // 'validation.level'=>'log'
    ]);

它返回的内容：

访问 https://api.sandbox.paypal.com/v1/payments/payment.NULL 时得到 Http 响应代码 400