Get dashboard summary with scope-aware KPI metrics

Example response

{
  "success": true,
  "data": {
    "volume_by_currency": [
      {
        "currency": "GBP"
      }
    ],
    "fees_by_currency": [
      {
        "currency": "GBP"
      }
    ],
    "next_payout_by_currency": [
      {
        "currency": "GBP"
      }
    ]
  }
}