500 INTERNAL_SERVICE_ERROR when I get Sale object

[EvansKim]

 Here is my code.

<?php
namespace App\Modules\Admin\Models\PaymentGateway;

use App\Mail\ErrorAlarm;
use App\Modules\Admin\Models\Order;
use App\Modules\Admin\Models\Payment;
use Illuminate\Http\Request;
use PayPal\Api\Amount;
use PayPal\Api\Details;
use PayPal\Api\Payer;
use PayPal\Api\PaymentExecution;
use PayPal\Api\RedirectUrls;
use PayPal\Api\RefundRequest;
use PayPal\Api\Sale;
use PayPal\Api\Transaction;
use PayPal\Auth\OAuthTokenCredential;
use PayPal\Exception\PayPalConnectionException;

class PaypalGateway implements PaymentGatewayInterface
{
    protected $config;
    public function __construct()
    {
        if( env("APP_ENV") == "production" ){
            $client_id = config('services.paypal.client_id');
            $secret = config('services.paypal.client_secret');
            $EndPoint = 'https://api.paypal.com';
            $mode = 'live';
        }else{
            $client_id = config('services.paypal_sandbox.client_id');
            $secret = config('services.paypal_sandbox.client_secret');
            $EndPoint = 'https://api.sandbox.paypal.com';
            $mode = 'sandbox';
        }
        $apiSetup = new  \PayPal\Rest\ApiContext(
            new OAuthTokenCredential(
                $client_id,
                $secret
            )
        );
        $apiSetup->setConfig(array(
            'mode' => $mode,
            'service.EndPoint' => $EndPoint,
            'log.LogEnabled' => true,
            'log.FileName' => storage_path('logs/paypal.log'),
            'log.LogLevel' => 'DEBUG'
        ));
        $this->config = $apiSetup;
    }

    /**
     * @param Order $order
     * @return \Illuminate\Http\RedirectResponse|\Illuminate\Routing\Redirector
     */
    public function redirect(Order $order)
    {
        $payer = new Payer();
        $payer->setPaymentMethod('paypal');

        $amount = new Amount();
        $amount->setCurrency('USD');
        $amount->setTotal( $order->unpaid_total );

        // This is the simple way,
        // you can alternatively describe everything in the order separately;
        // Reference the PayPal PHP REST SDK for details.

        $details = new Details();
        $details->setShipping( $order->shipping_cost );
        $details->setTax( $order->tax_amount );
        $details->setSubtotal( $order->products_amount - $order->discount );
        $amount->setDetails( $details );

        $transaction = new Transaction();
        $transaction->setAmount( $amount );
        $transaction->setInvoiceNumber( $order->order_code );
        $transaction->setDescription( 'Candleworks Home Fragrance DIY' );

        $redirectUrls = new RedirectUrls();
        $redirectUrls->setReturnUrl( route("shop.order.payment.callback") );
        $redirectUrls->setCancelUrl( route("shop.order.show", $order->id) );

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

        $response = $payment->create( $this->config );
        $redirectUrl = $response->getApprovalLink();

        \Session::put(['payment_order_id'=> $order->id]);

        return redirect( $redirectUrl );
    }

    /**
     * @param Request $request
     * @param Order $order
     * @return \Illuminate\Http\RedirectResponse
     */
    public function callback(Request $request, Order $order)
    {
        $id = $request->input('paymentId');
        $payment = \PayPal\Api\Payment::get($id, $this->config );

        $payer_id = $request->input('PayerID');

        $execution = new PaymentExecution();
        $execution->setPayerId($payer_id);

        try{
            $resultPayment = $payment->execute( $execution, $this->config );
        }catch ( PayPalConnectionException $e ){
            $json = json_decode( $e->getData() );
            alert()->error("Please try later. Paypal Server occurs some error.".$json->message ,"Try again");

            return redirect()->route("shop.order.show", $order->id);
        }

        if( $resultPayment->state == "approved" ) {
            $transections = $resultPayment->getTransactions();

            // Create purchase record in the database
            $order_code = $transections[0]->invoice_number;
            $related = $transections[0]->getRelatedResources();
            $sale = $related[0]->getSale();
            $saleId = $sale->getId();
            Payment::create([
                'order_id' => $order->id,
                'type' => 'paypal',
                'stripe_id' => $payer_id,
                'transaction_code' => $saleId,
                'amount' => $transections[0]->getAmount()->getTotal(),
                'memo' => 'Paypal Payment',
            ]);
            alert()->success("Payment Complete.", "Thank you");
        }
        return redirect()->route("shop.order.show", $order->id);
    }

    /**
     * @param Payment $payment
     * @return bool
     */
    public function refund(Payment $payment)
    {
        $sale = Sale::get($payment->transaction_code, $this->config);

        dump($sale);

    }
}

when i call function refund(), this error occur. I have no idea. Please help me.

[20-11-2017 16:22:18] PayPal\Core\PayPalHttpConnection : INFO: POST https://api.sandbox.paypal.com/v1/oauth2/token
[20-11-2017 16:22:23] PayPal\Core\PayPalHttpConnection : DEBUG: Request Headers    : POST /v1/oauth2/token HTTP/1.1, Host: api.sandbox.paypal.com, User-Agent: PayPalSDK/PayPal-PHP-SDK 1.12.0 (platform-ver=7.1.8; bit=32; os=Windows_NT_10.0; machine=i586; crypto-lib-ver=1.0.2k; curl=7.54.1), Authorization: Basic QVFscFF3R0tXclhJR3MyeXVSbzdwUzBrbklkUU56M1lpM3ZGek4xcFVlbkZaNzdyajVsSHlzUGZfdzhiY2NsTmdIY0tOUXhZc0V3d3gtQkU6RUduTFlpMmNaNTBrTFEzdnU3TmozdHIwSWZqVlNzR3hmMXFkVUV6Um9QWUNQLUFpMnZ5cFpiUkMxd3pEckpaanRZeVEycUVaS2FkNENUazE=, Accept: */*, Content-Length: 29, Content-Type: application/x-www-form-urlencoded, , 
[20-11-2017 16:22:23] PayPal\Core\PayPalHttpConnection : DEBUG: Request Data      : grant_type=client_credentials
--------------------------------------------------------------------------------------------------------------------------------

[20-11-2017 16:22:23] PayPal\Core\PayPalHttpConnection : INFO: Response Status     : 200
[20-11-2017 16:22:23] PayPal\Core\PayPalHttpConnection : DEBUG: Response Headers   : Date: Mon, 20 Nov 2017 07:22:19 GMT, Server: Apache, paypal-debug-id: 77188554ae35, X-PAYPAL-TOKEN-SERVICE: IAAS, HTTP_X_PP_AZ_LOCATOR: sandbox.slc, Paypal-Debug-Id: 77188554ae35, Set-Cookie: X-PP-SILOVER=; Expires=Thu, 01 Jan 1970 00:00:01 GMT, Vary: Authorization, Content-Length: 550, Connection: close, Content-Type: application/json, 
[20-11-2017 16:22:23] PayPal\Core\PayPalHttpConnection : DEBUG: Response Data  : {"scope":"https://uri.paypal.com/services/subscriptions https://api.paypal.com/v1/payments/.* https://api.paypal.com/v1/vault/credit-card https://uri.paypal.com/services/applications/webhooks openid https://uri.paypal.com/payments/payouts https://api.paypal.com/v1/vault/credit-card/.*","nonce":"2017-11-20T07:01:41Zf0xYkUvI5oXXj5wm0lZv6GSc6Me6xGNxNQMDyignZNI","access_token":"A21AAF59yHvnI6RyQg_PEd9EkKpOX0PXBCt_QXyK_V53d0XYDkv9gZ7DdC5goNN2XOoixvbfuHA4-upxBsIjtXTk5mCH3fTzA","token_type":"Bearer","app_id":"APP-80W284485P519543T","expires_in":31158}

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[20-11-2017 16:22:23] PayPal\Core\PayPalHttpConnection : INFO: GET https://api.sandbox.paypal.com/v1/payments/sale/2VW53071YA416114V
[20-11-2017 16:22:24] PayPal\Core\PayPalHttpConnection : DEBUG: Request Headers    : GET /v1/payments/sale/2VW53071YA416114V HTTP/1.1, Host: api.sandbox.paypal.com, Accept: */*, Content-Type: application/json, User-Agent: PayPalSDK/PayPal-PHP-SDK 1.12.0 (platform-ver=7.1.8; bit=32; os=Windows_NT_10.0; machine=i586; crypto-lib-ver=1.0.2k; curl=7.54.1), Authorization: Bearer A21AAF59yHvnI6RyQg_PEd9EkKpOX0PXBCt_QXyK_V53d0XYDkv9gZ7DdC5goNN2XOoixvbfuHA4-upxBsIjtXTk5mCH3fTzA, , 
[20-11-2017 16:22:24] PayPal\Core\PayPalHttpConnection : DEBUG: No Request Payload
--------------------------------------------------------------------------------------------------------------------------------

[20-11-2017 16:22:24] PayPal\Core\PayPalHttpConnection : INFO: Response Status     : 500
[20-11-2017 16:22:24] PayPal\Core\PayPalHttpConnection : DEBUG: Response Headers   : Date: Mon, 20 Nov 2017 07:22:24 GMT, Server: Apache, paypal-debug-id: 7e86cba31f260, Content-Language: *, X-SLR-RETRY: 500, X-SLR-RETRY-API: /v1/payments/sale/{id}, Connection: close, HTTP_X_PP_AZ_LOCATOR: sandbox.slc, Paypal-Debug-Id: 7e86cba31f260, Set-Cookie: X-PP-SILOVER=; Expires=Thu, 01 Jan 1970 00:00:01 GMT, Vary: Authorization, Content-Length: 187, Content-Type: application/json, 
[20-11-2017 16:22:24] PayPal\Core\PayPalHttpConnection : ERROR: Got Http response code 500 when accessing https://api.sandbox.paypal.com/v1/payments/sale/2VW53071YA416114V. {"name":"INTERNAL_SERVICE_ERROR","message":"An internal service error has occurred","information_link":"https://developer.paypal.com/docs/api/payments/#errors","debug_id":"7e86cba31f260"}
[20-11-2017 16:22:24] PayPal\Core\PayPalHttpConnection : DEBUG: 

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