Create a message
Creates an additional message (A/B test arm) on a draft broadcast by cloning the
control message’s default content (subject, body, sender).
Optionally provide from, reply_to and content (subject, preheader_text, name, body) fields
to override the cloned defaults. Editable only while the broadcast is a draft.
Authorizations
Accepts either a raw API key or Bearer <key>.
Headers
Optional dated API revision for the request. Must use YYYY-MM-DD format.
^\d{4}-\d{2}-\d{2}$"2026-03-01"
Path Parameters
Broadcast ID.
Body
Create an additional message (A/B arm) on a draft broadcast. The arm is
cloned from the control message's default content (subject, body, sender);
supplied fields override the clone. name, position, and other
derived/audience fields are rejected with 422 Validation error.
Response
Broadcast message created.
One message (A/B test arm) of a broadcast. from/reply_to are
email-only sender fields and are null for SMS/push messages.
Server-generated message name, for example Control or Variation A.
Sender email address (email messages only).
Reply-to email address (email messages only).

