Hello I have been working with the paypal php sdk.

I have been getting the following error when trying to create a Payment

PayPalConnectionException
Got Http response code 401 when accessing https://api.sandbox.paypal.com/v1/oauth2/token.

I am sure the $clientId and $clientSecret values are correct.

Running in sandbox mode - still in development phase.

Has anyone come across this?

My Code (with private info stripped)

use PayPal\Api\Amount;
use PayPal\Api\Item;
use PayPal\Api\ItemList;
use PayPal\Api\Payer;
use PayPal\Api\PayerInfo;
use PayPal\Api\Payment;
use PayPal\Api\RedirectUrls;
use PayPal\Api\Transaction as PayPalTransaction;
use PayPal\Auth\OAuthTokenCredential;
use PayPal\Exception\PayPalConnectionException;
use PayPal\Rest\ApiContext;

//$transaction represents a Transaction object stored in database
//$product represents a Product object stored in database

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

$itemList = new ItemList();

$itemList->addItem(
    (new Item)
        ->setName($product->getName())
        ->setDescription($product->getName())
        ->setSku($product->getSku())
);

$amount = (new Amount())
    ->setCurrency($transaction->getCurrency())
    ->setTotal($transaction->getTotal())
;

$ppTransaction = (new PayPalTransaction())
    ->setItemList($itemList)
    ->setAmount($amount)
    ->setReferenceId($transaction->getId())
;

$redirectUrls = (new RedirectUrls())
    ->setReturnUrl('http://.../S')
    ->setCancelUrl('http://.../F')
;

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

$payment = (new Payment())
    ->setIntent('sale')
    ->setPayer($payer)
    ->setRedirectUrls($redirectUrls)
    ->setTransactions([$ppTransaction])
;

$payment->create($apiContext);

return $payment->getId();

A dump of the underlying paypal curl request is as follows:

[
    "url"     => "https://api.sandbox.paypal.com/v1/oauth2/token"
    "method"  => "POST"
    "headers" => array:3 [
        0 => "User-Agent: PayPalSDK/PayPal-PHP-SDK 1.11.0 (platform-ver=7.0.7; bit=64; os=Linux_4.4.57-18.3-default; machine=x86_64; crypto-lib-ver=1.0.2j-fips; curl=7.37.0)"
        1 => "Authorization: Basic xxx="
        2 => "Accept: */*"
    ]
    "data" => "grant_type=client_credentials"
]