Fatal error with Stripe Checkout: Class 'Stripe' not found - payment

Question

I'm trying to implement Stripe Checkout into my website. I am using Composer, everything seems to go right, but when I add my private key into init.php line 17:
Stripe::setApiKey($stripe['private']);
PHP shows me the following error:
Fatal error: Class 'Stripe' not found in/Applications/MAMP/htdocs/stripe_payment/app/init.php on line 17
Here is the full file:
<?php
session_start();
//composer auto load
require_once 'vendor/autoload.php';
$_SESSION['user_id'] = 3;
$stripe = [
'publishable' => '..... my test key.....',
'private' => '..... my test key.....'
];
//when added brakes the code
Stripe::setApiKey($stripe['private']);
$db = new PDO('mysql:host=localhost;dbname=stripe_custom;','root','root');
$userQuery = $db->prepare("
SELECT id, username, email, premium
FROM users
WHERE id = :user_id
");
$userQuery->execute(['user_id' => $_SESSION['user_id']]);
$user = $userQuery->fetchObject();
?>
I presume that this is something small, but I'm a beginner and I can't figure it out. What am I doing wrong?

Answer 1

The latest releases of Stripe's PHP bindings (2.*) are now using Namespaces. This means that most of the API calls have now changed and for example:
Stripe::setApiKey("sk_test_XXX");
Stripe_Customer::create();
would become:
\Stripe\Stripe::setApiKey("sk_test_XXX");
\Stripe\Customer::create();
Otherwise, if you don't want to have to update your code you need to make sure that you download the legacy version (1.18.0).