Discrepancy between API endpoint /api/metric-aggregates/ and exported reporting data

Hey Klaviyo team,

We extracted data for one of our clients using endpoint /api/metric-aggregates/.

However, the client complains about data discrepancy. For example, campaign with ID 01HBAV7QKRFSJ5NP8A12KC6SA4 in the exported reporting data has “Total Opens” = 15300:

But statistics for metric "Opened Email" (TaxZXt) returned 13462:

POST /api/metric-aggregates/ HTTP/1.1
Host: a.klaviyo.com
Authorization: Klaviyo-API-Key {{api_key}}
revision: 2023-10-15
Accept: application/json
Content-Type: application/json
Content-Length: 407

{
  "data": {
    "type": "metric-aggregate",
    "attributes": {
      "metric_id": "TaxZXt",
      "interval": "month",
      "measurements": [
        "count"
      ],
      "filter": [
        "greater-or-equal(datetime,2023-10-01T00:00:00)",
        "less-than(datetime,2023-11-01T00:00:00)"
      ],
      "by": [
        "$message"
      ],
      "page_size": 500,
      "timezone": "UTC"
    }
  }
}

Part of the response for campaign with ID 01HBAV7QKRFSJ5NP8A12KC6SA4:

                {
                    "dimensions": [
                        "01HBAV7QKRFSJ5NP8A12KC6SA4"
                    ],
                    "measurements": {
                        "count": [
                            13462.0
                        ]
                    }
                },

Could you please clarify what’s a reason for the discrepancy?

Kind regards,

Evgeniy