Error 401 in PayPal sandbox because of client id (Braintree)

I wrote a simple PHP script to make PayPal popup payment button :

<!-- Load the required checkout.js script -->
<script src="https://www.paypalobjects.com/api/checkout.js" data-version-4></script>

<!-- Load the required Braintree components. -->
<script src="https://js.braintreegateway.com/web/3.87.0/js/client.min.js?"></script>
<script src="https://js.braintreegateway.com/web/3.87.0/js/paypal-checkout.min.js"></script>

<script type="text/javascript" src="js/jquery.min.js"></script>

<script>

<?php 

require_once 'vendor/lib/Braintree.php';

$access_token = 'access_token$sandbox$...3';

$gateway = new Braintree\Gateway([
    'accessToken' => $access_token,
]);

$clientToken = $gateway->clientToken()->generate();


?>

paypal.Button.render({
  braintree: braintree,
  client: {
    //production: '<?= $clientToken ?>',
    sandbox: '<?= $clientToken ?>'

  },
  env: 'sandbox', 
  style: {
          shape: 'rect',
          color: 'blue',
          layout: 'horizontal',
          label: 'pay',
          
        },

  payment: function (data, actions) {
    return actions.braintree.create({

      flow: 'checkout', // Required
      amount: 10.00, // Required
      currency: 'USD', // Required
      intent: 'sale',
      enableShippingAddress: false
    });
  },

  onAuthorize: function (payload) {
        
    $.ajax({

     url : 'verify.php',
     type : 'POST',
     data: { 
        "payment_method_nonce": payload.nonce
      },
     success : function (result) {
        alert(result);
     },
     error : function () {
        alert(result);
     }

   });

  },
}, '#paypal-button');

</script>

<div id="paypal-button"></div>

All steps (including settle) are working but the problem is that I have some JS errors with code 401 from PayPal server because of Client Id as below :

https://pasteboard.co/PABp8HzbdfhB.png

Failed to load resource: the server responded with a status of 401 ()

I searched in PayPal & Braintree docs but couldn't find how to pass my client id. All manuals are about older versions of SDK!

So what's the solution?

Link a PayPal sandbox account in the Braintree gateway settings, Processing.