Data discrepancy between API and dashboard

Hi, i’m using the latest stable version of Klaviyo API to fetch number of opened emails, here’s the API request config

{
  method: 'POST',
  baseURL: 'https://a.klaviyo.com/api/metric-aggregates/',
  headers: {
    accept: 'application/json',
    Authorization: `Klaviyo-API-Key ${apiKey}`,
    revision: '2023-06-15',
    'content-type': 'application/json',
  },
  data: JSON.stringify({
    data: {
      type: 'metric-aggregate',
      attributes: {
        measurements: ['unique'],
        filter: [`greater-or-equal(datetime,${start_date})`, `less-than(datetime,${end_date})`],
        by: ['$message'],
        metric_id: metric_id,
        interval: 'month',
      },
    },
  }),
};

i then sum the values based on campaign, but the data is not accurate when compared to the dashboard, in the dashboard no. of opened emails is higher than what i get from the API

Is this a bug or is there any explanation for these discrepancies? same is happening with other metrics as well like ‘Clicked Email’, ‘Active on Site’, etc