Paypal API Rest, integration in Symfony project - php

Question

I'm coming to desperatly try to find help about a error that even the paypal technical support still didn't achieve to understand...
This is the error returned : "Attempted to load class "ApiContext" from namespace "PayPal\Rest".
Did you forget a "use" statement for another namespace?"
I installed the paypal api via composer, and here is the code using this api. I followed the documentation steps by steps, so I really don't understand this error... the use statements are all there... :
<?php
namespace PlatformBundle\Controller;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use PayPal\Api\Payer;
use PayPal\Api\Item;
use PayPal\Api\ItemList;
use PayPal\Api\Details;
use PayPal\Api\Amount;
use PayPal\Api\Transaction;
use PayPal\Api\RedirectUrls;
use PayPal\Api\Payment;
use PayPal\Auth\OAuthTokenCredential;
use PayPal\Rest\ApiContext;
class PaypalController extends Controller
{
private function paypalKeys()
{
return new ApiContext(
new OAuthTokenCredential(
'AUWLQ9xMRA54XpqgX_Bbd0koHkIzfAFnZSPXipGbIZAqVnJCaWj5B4hga5dbd2UE0diElegudMDR9dj0',
'EPStewzop-DjMhdyvw51TJBnpZUHt6hGahwmRSDljIhYmDVGMPXsAV0oWoMiCcQpVdXsyOdnZJN1yRZC'
)
);
}
public function chargeAction()
{
$this->paypalKeys();
$price = 10;
$total = $price;
$payer = new Payer();
$payer->setPaymentMethod('paypal');
$item = new Item();
$item->setName('transfer')
->setCurrency('eur')
->setQuantity(1)
->setPrice($price);
$itemList = new ItemList();
$itemList->setItems([$item]);
$details = new Details();
$details->setShipping(0)
->setSubtotal($price);
$amount = new Amount();
$amount->setCurrency('eur')
->setTotal($total)
->setDetails($details);
$transaction = new Transaction();
$transaction->setAmount($amount)
->setItemList($itemList)
->setDescription('Description')
->setInvoiceNumber(uniqid());
$redirectUrls = new RedirectUrls();
$redirectUrls->setReturnUrl('http://localhost/dublin/web/app_dev.php/admin')
->setCancelUrl('http://localhost/dublin/web/app_dev.php/cancel');
$payment = new Payment();
$payment->setIntent('sale')
->setPayer($payer)
->setRedirectUrls($redirectUrls)
->setTransactions([$transaction]);
// try {
$payment->create($this->paypalKeys());
// } catch (Exception $e) {
// die($e);
// }
//
// return new Response('true');
// echo $approvalUrl = $payment->getApprovalLink();
}
}
Thanks for your help...