How do I update a board item's start date through the API?

Short answer: The due-date endpoint only sets the due date. To change the start date, send the _start_date system field in the item update call.

Why it happens

• The board API has a dedicated endpoint for the due date, but not for the start date.
• The start date is a system field you set through the general item update.

How to fix it

1. Call Update board item custom fields:

   POST https://<subdomain>.kissflow.com/case/2/<account_id>/<case_id>/<item_id>/<status_id>

2. Send the start date in the body:

   { "_start_date": "2026-08-15T09:00:00Z" }

3. Use an ISO 8601 date-time, the same format the due-date endpoint uses.

The update is partial, so only the fields you send change. See the API reference.