PayPal PHP API SDK -设置个人购买电子邮件地址

我想为购买产品的人设置电子邮件地址。这是我目前为止得到的(根据文档):

$payer = new \PayPal\Api\Payer();
$payer  ->setPaymentMethod('paypal');

$amount = new \PayPal\Api\Amount();
$amount->setTotal($order['totals']['grand']);
$amount->setCurrency('GBP');

$itemList = new \PayPal\Api\ItemList();

$shipping_address = new \PayPal\Api\ShippingAddress();
$shipping_address->setRecipientName($order['shipping']['name']);
$shipping_address->setLine1($order['billing']['add1']);
$shipping_address->setLine2($order['billing']['add2']);
$shipping_address->setCity($order['shipping']['add3']);
$shipping_address->setPostalCode($order['shipping']['postcode']);
$shipping_address->setCountryCode(countryData($order['shipping']['countryID'],"code"));
$shipping_address->setPhone($order['shipping']['telephone']);
$itemList->setShippingAddress($shipping_address);

$transaction = new \PayPal\Api\Transaction();
$transaction->setAmount($amount)->setItemList($itemList);

$redirectUrls = new \PayPal\Api\RedirectUrls();
$redirectUrls   ->setReturnUrl("https://example.com/shop/thank-you/")
                ->setCancelUrl("https://example.com/shop/cancelled/");

$payment = new \PayPal\Api\Payment();
$payment->setIntent('sale')
        ->setPayer($payer)
        ->setTransactions(array($transaction))
        ->setRedirectUrls($redirectUrls);  

try {
    $payment->create($apiContext);
    predump(json_decode($payment));

    echo "\n\n<a href='".$payment->getApprovalLink()."'>Redirect user to approval_url</a>\n";
}
catch (\PayPal\Exception\PayPalConnectionException $ex) {
    // This will print the detailed information on the exception.
    //REALLY HELPFUL FOR DEBUGGING
    echo $ex->getData();
}

我可以从Paypal推出的文档的集锦中收集,并且从Google的许多不同的页面中,我想在PayRe[()中设置电子邮件地址( $payer )我该怎么做?

请帮忙。