How do I get shipping lines (shipping method/carrier) with a fulfillment order?

[Philipp4]

Hi,

I'm trying to switch to fulfillment orders/requests for my private app and it works fine so far. 

The only problem I have is how to get the shipping lines (or shipping carrier) that was selected by the customer? 

From my understanding of the documentation (https://shopify.dev/api/admin/rest/reference/shipping-and-fulfillment/fulfillmentorder#show-2021-07)... it should be in the "merchant_requests" array. But all I get is this:

"merchant_requests": [
 {
  "message": null,
  "request_options": {
   "notify_customer": false
  },
  "sent_at": "2021-08-02T14:10:59+02:00",
  "kind": "legacy_fulfill_request"
 }
]

(the request was sent with the Shopify Admin UI)

Based on this info: https://shopify.dev/changelog/delivery-method-property-in-the-rest-fullfillmentorder-resource There should also be a delivery_method value in the Fulfillment Order. 

But for my Fulfillment-Orders its always null:

"delivery_method": null

Am I looking at the wrong place? 

Thanks!