curl --request GET \
  --url https://api.prime.coinbase.com/v1/portfolios/{portfolio_id}/margin_conversions

{
  "conversions": [
    {
      "conversion_details": [
        {
          "symbol": "BTC",
          "tf_balance": "20000",
          "notional_tf_balance": "4000",
          "converted_balance": "1000",
          "notional_converted_balance": "1000",
          "interest_rate": "0.1",
          "conversion_rate": "0.1"
        }
      ],
      "short_collateral": {
        "old_balance": "1000",
        "new_balance": "1000",
        "loan_interest_rate": "0.1",
        "collateral_interest_rate": "0.1"
      },
      "conversion_datetime": "2023-05-01T12:00:00.000Z",
      "portfolio_id": "<string>"
    }
  ]
}