Fulfillment API returning 400 "Required parameter missing or invalid"

[JainShina]

Hello There,

Trying to fulfill an order with the help of fulfillments.json, but it is returning 400 - "Required parameter missing or invalid". 

It's POST request with the URL https://{{shopify_base_url}}/admin/api/{{shopify_webhook_version}}/fulfillments.json and 

Request Body 

{

  "fulfillment": {

    "line_items_by_fulfillment_order": [

      {

        "fulfillment_order_id": 6X5X990XXX69,

        "fulfillment_order_line_items": [

          {

            "id": 14X5X8XXXX5XXX,

            "quantity": 1

          }

        ]

      }

    ],

    "message": "Yay! The package was shipped this morning.",

    "notify_customer": false,

    "origin_address": {

      "country_code": "US"

    },

    "tracking_info": {

      "company": "Canada Post",

      "number": "123456789",

      "url": "tracking_url"

    }

  }

}

Not able to understand why the API call returning request parameter is missing or have incorrect value.

Looking forward for the help.

Thank you!