Setting the location_id failed when creating a new fullfillment

Payments + Shipping & Fulfilment
1

When I retrieve the order via /orders/[order_id]/fulfillment_orders.json, the json object shows the default location_id under assigned_location. I think this is done by creating a new order.

Then, when I create a new fulfillment using the endpoint /fulfillments.json, setting another location_id the order ends up being processed with the default location_id. This is my payload:

{
  "fulfillment": {
    "notify_customer": true,
    "location_id": [location_id],
    "line_items_by_fulfillment_order": [
      {
        "fulfillment_order_id": 1234567890,
        "fulfillment_order_line_items": [
          {
            "id": 1234567890,
            "quantity": 1
          }
        ]
      }
    ]
  }
}

Am I missing a setting or action? Hopefully, someone recognizes this or can point me in the right direction