You can find the api_url & product_key in the Software tab of your product. Please the section 4.3 of the product documentation.

api_url
URL of the server Rest API.
product_key
Public product key of the product related to your plugin.
dir
Don’t change this unless you know what you’re doing.
rest_namespace
Enable Rest API endpoints to handle your license.
parent_menu_slug
Include the slug of your plugin’s main menu to attach the license page or include false to disable it completely.
license_url
Include a custom license URL. This is specially useful if you’ve disabled the parent_menu_slug.

1. Download the license client repo from this link or integrate via composer.

2. Include the licenseClient folder in your vendor/licenseClient folder of your plugin.

3. Create a file called ql_license_client_integration.php

4. Go to the main file of your plugin and include this code.
require_once 'ql_license_client_integration.php';

5. Include this code in the ql_license_client_integration.php

<?php

if ( ! function_exists( 'your_plugin_license_client_integration' ) ) {

function your_plugin_license_client_integration() {

global $your_plugin_license_client;

if ( ! isset( $your_plugin_license_client ) ) {

require_once 'vendor/license-client/index.php';

$your_plugin_license_client = ql_license_client(
array(
'api_url' => 'https://yoursite.com/wp-json/wc/wdd/',
'product_key' => 'xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx',
'dir' => __DIR__,
// 'rest_namespace' => 'your_plugin',
// 'parent_menu_slug' => 'your_plugin_menu_slug',
// 'license_url' => admin_url( 'admin.php?page=your_plugin_license_page' ) ),
)
);
}

return $your_plugin_license_client;
}

your_plugin_license_client_integration();
}