Unable to update Fulfillment Status using REST API

Hello there,

I am trying to update the fulfillment for an order using REST-API.

API used: POST /admin/api/2021-07/orders/{order_id}/fulfillments.json

By using above API there is no change in my order.

It returns an HTML with the link to continue. I tried this through POSTMAN.

Please help me through this.

Thanks.