Google API php client

hi, I am trying to use the google client api. Following the instructions of developers.google.com/sheets/api/quickstart/php, I can't get to instantiate the client object.

I put this code in my controller:

PHP Code:

<?php namespace App\Controllers;

require_once   (__DIR__ . './../ThirdParty/googleApi/vendor/autoload.php');

class GoogleSheetData extends BaseController
{
    public function index()
    {
        putenv('GOOGLE_APPLICATION_CREDENTIALS='.(__DIR__ . './../ThirdParty/xxxxxx.json'));
        $client = new Google_Client();
.
.
. 


but I get the error:
Class 'App\Controllers\Google_Client' not found

I appreciate any help, thanks

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