curl --request GET \
  --url https://api.asksurf.ai/gateway/v1/market/etf

{
  "data": [
    {
      "flow_usd": 123,
      "price_usd": 123,
      "timestamp": 123,
      "etfs": [
        {
          "flow_usd": 123,
          "ticker": "<string>"
        }
      ]
    }
  ],
  "meta": {
    "cached": true,
    "credits_used": 123
  },
  "$schema": "<string>"
}