{
  "recipients": ["+255614853618", "+255712345678"],
  "message": "Hello, this is a quick message",
  "sender_id": "MIFUMO"
}

{
  "success": true,
  "message": "SMS sent to 2 recipients",
  "sent": 2,
  "failed": 0,
  "message_ids": [
    "550e8400-e29b-41d4-a716-446655440000",
    "550e8400-e29b-41d4-a716-446655440001"
  ]
}