Send up to 1000 SMS in one request. Each item is validated independently — valid items are queued and returned in accepted (each with its own message_id), invalid ones are returned in rejected (partial success). Delivery status is sent per item to your configured webhook (events sms.delivered / sms.undelivered / sms.error). The batch is charged against the per-minute rate limit by its item count. Requires the SMS & Voice feature to be enabled for your account by the Clint team.