curl https://zeplo.ai/api/campaigns/1/analytics \
  -H "Cookie: connect.sid=s%3A7HImZ-T2BxWSbUsf9dtWdOlBW4rVuORO.5J0Do0NyvBu%2BkTvu1aHvtNs00BKhkpUKTwiokLS0cpw"

{
  "success": true,
  "data": {
    "campaignId": 1,
    "campaignName": "New Year Promo",
    "status": "completed",
    "summary": {
      "totalRecipients": 500,
      "sent": 480,
      "delivered": 470,
      "read": 320,
      "replied": 45,
      "failed": 20
    },
    "deliveryRate": 97.9,
    "readRate": 68.1,
    "replyRate": 9.6,
    "failureRate": 4.2,
    "timeline": [
      {
        "timestamp": "2026-01-01T09:00:00Z",
        "event": "started",
        "count": 0
      },
      {
        "timestamp": "2026-01-01T09:05:00Z",
        "event": "sent",
        "count": 240
      },
      {
        "timestamp": "2026-01-01T09:15:00Z",
        "event": "completed",
        "count": 480
      }
    ],
    "failedRecipients": [
      {
        "contactId": 15,
        "phone": "919876543215",
        "error": "Invalid phone number",
        "errorCode": 131009
      }
    ]
  }
}