Failed opening required 'vendor/autoload.php' error when trying require_once('vendor/autoload.php');

Trying to get Stripe library up and running. Get failed opening required 'vendor/autoload.php' error.

autoload.php is there in /vendor

ran composer update, then composer install , didn't help.

config.php

    <?php

require_once('vendor/autoload.php');

    $stripe = array(
      "secret_key"      => "XXXXXXXXXXXXXXXXXXXXXX",
      "publishable_key" => "XXXXXXXXXXXXXXXXXXXXXX"
    );

    \Stripe\Stripe::setApiKey($stripe['secret_key']);

?>

via Chebli Mohamed