To change status of the post you need to know ID of that post. You can do that by searching post.
Post request
curl -H 'Accept: application/json' -H "Content-Type: application/json"\
-X POST \
-d '{"post_id": <POST_ID>, "status_name": "<STATUS_NAME>", "comment": "<COMMENT CONTENT>", "notify': true}'\
-H "Authorization: Bearer <API_TOKEN>"\
https://productroad.com/api/v1/status/change/
Example response
{"status": "Success", "post_id": <POST_ID>, "comment_id": "<ID OF CREATED COMMENT>"}