您好，我正在尝试从URL获取coinbase API汇率，但是json.net似乎无法格式化JSON文件以读取子级

这是引发错误的方法

public string CalculateCoinValue(Coinbase connector)
{
    //bool valid = connector.rates.isValid;

    string cryptoExchangeRate;

    if (connector.rates != null)
    {
        cryptoExchangeRate = (string)connector.rates["data"]["currency"]["rates"][Settings.defualtCrypto.ToUpper()];

    }

    return "";
}

这是im用于获取JSON数据的方法，该数据将其存储在Coinbase类中的JObject中

public async Task<JObject> GetExchangeRatesAsync()
{

    HttpClient webClient = new HttpClient();
    string url = string.Format("https://api.coinbase.com/v2/exchange-rates?currency=" + Settings.defaultCurrency);
    HttpResponseMessage coinbaseJsonRaw = await webClient.Getasync(url);
    return JObject.Parse(await coinbaseJsonRaw.Content.ReadAsStringAsync());
}

该怎么办，我做错了什么？