Why isn't my PHP SDK code fulfilling an order correctly?

[DomenicoToma]

Hi,

I'm trying to fullfull an order through the PHP SDK.

Here's my code:

$shopify = new PHPShopify\ShopifySDK($config);
$shopify->Order($orderId)->put([
     "fulfillment_status" => "fulfilled",
]);

...but it doesn't work.

I've checked the permissions and they're ok. If I print the result I get che entire order entity but with no changes on the fulfillment_status field.

What could be wrong?

Thank you in advance.