Php – Google APIClient Class not found using Composer

I´m using composer to install the the google api client Packagist Google API Client.

After I installed it using composer require google/apiclient it installed like normal.
After that I tried to use it in the example below

<?php
use GoogleServiceShoppingContent;
use GoogleAuthCredentialsServiceAccountCredentials;

/**
 *
 */
class GoogleShoppingContentAPI
{
  private $service;

  public function __construct($credentialsPath) {
    // Create the credentials object
    $credentials = new ServiceAccountCredentials(
        ShoppingContent::CONTENT,
        $credentialsPath
    );
    // Create the Shopping Content Service with the credentials
    $this->service = new ShoppingContent(['credentials' => $credentials]);
  }

  public function getProducts($merchantID)
  {
    try {
      // Fetch a list of products
      $products = $this->service->products->listProducts($merchantID);
      // Return the product data as an array
      return $products->getResources();
    } catch (GoogleServiceException $e) {
      throw new Exception("Error: " . $e->getMessage());
    }
  }
}

However when running the code it prints out this error:

Class Fatal error: Uncaught Error: Class "GoogleAuthCredentialsServiceAccountCredentials" not found in /Users/Shared/www/inc/google.inc.php on line 15

It is in our autoload and our autoload is required before running the code aboved.
The Google namespace isnt occupied by another package aswell.

I already looked through our project and did not found any duplicate namespaces related to google.
Also reinstalling aswell composer update did not changed anything.