How to add message statuses to a board using REST API?

Hi all,

the documentation says that you should be able to add a message status to a board by posting something like this:

curl -v -d message_status.is_completed=false -d message_status.key="Unassigned" -d message_status.name="Unassigned"  -d restapi.session_key=... $LITHIUMBASE/restapi/vc/boards/id/$BOARD/message_statuses/available/add

However, this gives me the error 511, "A required query string argument is missing."

The documentation only mentions message_status.key and message_status.name as being required.

What am I doing wrong?

Bonus question: What are the values that message_status.type can get?

Thanks!