fulfillment_orders empty response even though all access scopes are set

[JayMan]

Hi all,

I have a Shopify Store that has been normally running for some years. 
As I happen to be a developer, I have created Apps for my store in the past, to automate some processes using Shopify API with the Admin API token from my Apps. Those are not public apps. I have created them by logging in to my store and navigating to Settings > Apps and sales channels > Develop Apps.

For a next automation I need to update the fulfillment status & tracking number of orders. I've read all relevant docs (e.g. https://shopify.dev/docs/api/admin-rest/2024-04/resources/fulfillmentorder#get-orders-order-id-fulfi...), granted (literally) all access scopes to my app but can not get the fulfillment_orders.json endpoint to return anything but an empty array (e.g. GET https://{myStore}.myshopify.com/admin/api/2024-04/orders/{orderId}/fulfillment_orders.json) . As per docs, a fulfillment order is always created upon the creation of the order. Searching for this online has not been helpful. Almost every similar issue I have read through was solved by either granting more access scopes.

Through this operation I need to grab the fulfillment_order_id to use it later for this automation. 

What am I missing here? Any help is greatly appreciated.