curl --request GET \
  --url https://external-api.kalshi.com/trade-api/v2/series/fee_changes

{
  "series_fee_change_arr": [
    {
      "id": "<string>",
      "series_ticker": "<string>",
      "fee_multiplier": 123,
      "scheduled_ts": "2023-11-07T05:31:56Z"
    }
  ]
}