A newsletter still has to be written and scheduled by hand. The API can add people and send one transactional email, but it cannot create a broadcast, set the subject and HTML, choose the segment, and set a send time. If you run campaigns from another tool, that last step stays manual. Please add create, schedule, and cancel for broadcasts, and for the email they send, on the public API, with the same unsubscribe, timezone, and reporting behavior as the Broadcasts screen.