How to set quantity of items to buy in Paypal Orders API?

I can create a PayPal Order inside my Laravel Controller like so:

$provider = PayPal::setProvider();
$provider->setApiCredentials(config('paypal'));
$token = $provider->getAccessToken();
$provider->setAccessToken($token);

$price = '2';
$currency = '';

$order = $provider->createOrder([
    'intent' => 'CAPTURE',
    'purchase_units' => [
        [
            'amount' => [
                'currency_code' => 'EUR',
                'value' => $price
            ],
        ]
    ]
]);

return response()->json($order);

but when I try to add a quantity property (quantity of the same item to be bought):

$provider = PayPal::setProvider();
$provider->setApiCredentials(config('paypal'));
$token = $provider->getAccessToken();
$provider->setAccessToken($token);

$price = '2';
$currency = '';

$order = $provider->createOrder([
    'intent' => 'CAPTURE',
    'purchase_units' => [
        [
            'amount' => [
                'currency_code' => 'EUR',
                'value' => $price
            ],
            'items' => [
                'name' => 'photo',
                'quantity' => '5'
            ]
        ]
    ]
]);

return response()->json($order);

I’m getting a warning:

click_initiate_payment_reject {err: 'Error: Expected an order id to be passedn    at ht…ng=card,giropay,sepa,sofort&currency=EUR:2:14811)', timestamp: '1657705690794', referer: 'www.sandbox.paypal.com', sdkCorrelationID: 'f857450e442be', sessionID: 'uid_c2bc52c0a2_mdk6mzg6mta', …}

and this error:

Uncaught Error: Expected an order id to be passed
    at https://www.sandbox.paypal.com/smart/buttons?

Am I setting the quantity incorrectly? What’s the right way to do it? I really just want to send the total quantity of purchases, so that it’s displayed in the paypal checkout.