curl -sS -X POST 'https://matrix.example.com/_synapse/admin/v1/send_server_notice' -H "Authorization: Bearer $ACCESS_TOKEN" -d '{"user_id":"@alice:example.com","content":{"msgtype":"m.text","body":"Please review our terms"}}'

Delivers a notice into the user's server notices room, which admins use for terms updates or policy messages. Requires the server_notices section to be configured in homeserver.yaml first. The body's content field follows the normal message format. Prefer the PUT form with a transaction ID when retrying to avoid duplicates.