I Can't update a fulfilment on an existing order.

[pickandship]

Hi I have a private app and have enabled all the requirements needed.

I can update/read products, get order, get  fulfilment ID

I have the correct fulfilment & order IDs

When I try to update a fulfilment ID I get a 406Not Acceptable error


curl --location --request PUT 'https://myShop.myshopify.com/admin/api/2024-10/orders/5924257104212/fulfillments/5329461772628.json' \
--header 'Content-Type: application/json' \
--header 'X-Shopify-Access-Token: myToken' \
--data '{
"fulfillment": {
"tracking_number": "new_tracking_number_123",
"tracking_urls": ["https://trackingurl.com/track/new_tracking_number_123"],
"tracking_company": "New Carrier Name",
"notify_customer": true
}
}'

I am updating an old order ( so not to cause any issues ) Could it be archived ?

Also I cannot create a fulfilment ( I presume because the order already has a fulfilment done)
Any ideas please.