Paypal integration now required Braintree SDK, to use the Braintree SDK, you will require the Client_Token generate from the server.

What is Client Token?

A client token is a signed data blob that includes configuration and authorization information required by the Braintree client SDK. These should not be reused; a new client token should be generated for each request that’s sent to Braintree. For security, we will revoke client tokens if they are reused excessively within a short time period.

Your server is responsible for generating the client token, which contains all of the necessary configuration information to set up the client SDKs. When your server provides a client token to your client, it authenticates the application to communicate directly to Braintree.

How to create the server-side client token generator using PHP? Here some easy and straight forward codes you can use.

P/S: this code work for me, if you have simple easier and better please share.

First of all, you need to download the PHP Library from Braintree Developer site

Then, include it by

require_once '/lib/Braintree.php';

follow by instantiate a Braintree Gateway like this

$gateway = new Braintree_Gateway([
'environment' => 'sandbox',
'merchantId' => '[paypal-merchant-id]',
'publicKey' => '[paypal-public-key]',
'privateKey' => '[paypal-private-key]'

use below code to generate the key

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