Sends the same SMS or MMS message to a large list of recipients in a single API call. The recipients array must contain between 100 and 50,000 entries with unique phone numbers. The sender number (from) must be an active number assigned to your account. For SMS, provide a body (max 640 characters). For MMS, provide a mediaUrl pointing to a publicly accessible media file; the media is downloaded, validated, and attached to every message in the broadcast. You may include both body and mediaUrl for MMS with text. The broadcast is queued as a background job — the response includes a broadcast id and initial status of queued. An optional idempotencyKey prevents duplicate broadcast submissions.
Content compliance: Message content is validated against messaging compliance rules (SHAFT, phishing, etc.). Messages that violate these rules are rejected with error code 33019.
Rate limit: 5 requests per 60-second window. Every response includes X-RateLimit-Limit, X-RateLimit-Remaining, and X-RateLimit-Reset headers. When the limit is exceeded, a 429 response is returned with a Retry-After header.