Controller/Adminhtml/Ajax/Fbtoken.php

<?php
/**
 * Copyright (c) Meta Platforms, Inc. and affiliates. All Rights Reserved
 */

namespace Facebook\BusinessExtension\Controller\Adminhtml\Ajax;

use Magento\Framework\Stdlib\DateTime\DateTime;

class Fbtoken extends AbstractAjax
{
    // phpcs:disable Generic.CodeAnalysis.UselessOverridingMethod
    public function __construct(
        \Magento\Backend\App\Action\Context $context,
        \Magento\Framework\Controller\Result\JsonFactory $resultJsonFactory,
        \Facebook\BusinessExtension\Helper\FBEHelper $fbeHelper
    ) {
        parent::__construct($context, $resultJsonFactory, $fbeHelper);
    }

    public function executeForJson()
    {
        $old_access_token = $this->_fbeHelper->getConfigValue('fbaccess/token');
        $response = [
        'success' => false,
        'accessToken' => $old_access_token
        ];
        $access_token = $this->getRequest()->getParam('accessToken');
        if ($access_token) {
            $this->_fbeHelper->saveConfig('fbaccess/token', $access_token);
            $response['success'] = true;
            $response['accessToken'] = $access_token;
            if ($old_access_token != $access_token) {
                $this->_fbeHelper->log("Updated Access token...");
                $datetime = $this->_fbeHelper->createObject(DateTime::class);
                $this->_fbeHelper->saveConfig(
                    'fbaccesstoken/creation_time',
                    $datetime->gmtDate('Y-m-d H:i:s')
                );
            }
        }
        return $response;
    }
}