curl --request GET \
  --url https://futures.kraken.com/derivatives/api/v3/historical-funding-rates

{
  "result": "success",
  "serverTime": "2022-06-28T09:29:04.243Z",
  "rates": [
    {
      "timestamp": "2022-06-28T00:00:00.000Z",
      "fundingRate": -8.15861558e-10,
      "relativeFundingRate": -0.000016898883333333
    },
    {
      "timestamp": "2022-06-28T04:00:00.000Z",
      "fundingRate": -2.6115278e-11,
      "relativeFundingRate": -5.40935416667e-7
    },
    {
      "timestamp": "2022-06-28T08:00:00.000Z",
      "fundingRate": -4.08356853e-10,
      "relativeFundingRate": -0.000008521190625
    }
  ]
}