Accepts either a raw secret key or Bearer <sk_KEY>.
Optional dated API revision for the request. Must use YYYY-MM-DD format.
^\d{4}-\d{2}-\d{2}$"2026-03-01"
Campaign message ID.
Campaign content record ID.
Returns campaign message content, including the actual html, mjml or other values.
null for the default content variant.
Full body: exactly one of mjml, html, text or payload is set.