Change Json string to SnakeCase using SnakeCaseNamingStrategy in ASP.Net

I have a simple nested response using object property not model.

I want to change response json object to snake case

I have tried to convert using SnakeCaseNamingStrategy but still failed or nothing change at all

I hope someone can Help me, Thanks

{"PartnerInquiryId":"0f8e0a8a9fcf427ca5e534084c63bc91","ClientNumber":"04263123010394","ProductCode":"string","ResponseCode":"00","Message":"Success","DueDate":"21/01/2023","BillGenerationDate":"","IsOpenAmount":"","AdminFee":"2225","TotalAmount":"220225","Timestamp":"2023-05-05","BillDetails":[{"Name":"Customer Name","Value":"RIZA SAPTO PUTRO","IsPii":true,"IsShow":true},{"Name":"Bill To","Value":"1","IsPii":false,"IsShow":true},{"Name":"Penalty","Value":"0","IsPii":false,"IsShow":true},{"Name":"Interest","Value":"0","IsPii":false,"IsShow":true},{"Name":"Installment","Value":"0","IsPii":false,"IsShow":true}]}

the result is :

{
  "PartnerInquiryId": "0f8e0a8a9fcf427ca5e534084c63bc91",
  "ClientNumber": "04263123010394",
  "ProductCode": "string",
  "ResponseCode": "00",
  "Message": "Success",
  "DueDate": "21/01/2023",
  "BillGenerationDate": "",
  "IsOpenAmount": "",
  "AdminFee": "2225",
  "TotalAmount": "220225",
  "Timestamp": "2023-05-05",
  "BillDetails": [
    {
      "Name": "Customer Name",
      "Value": "RIZA SAPTO PUTRO",
      "IsPii": true,
      "IsShow": true
    },
    {
      "Name": "Bill To",
      "Value": "1",
      "IsPii": false,
      "IsShow": true
    },
    {
      "Name": "Penalty",
      "Value": "0",
      "IsPii": false,
      "IsShow": true
    },
    {
      "Name": "Interest",
      "Value": "0",
      "IsPii": false,
      "IsShow": true
    },
    {
      "Name": "Installment",
      "Value": "0",
      "IsPii": false,
      "IsShow": true
    }
  ]
}

public static string StringTOSnakeCaseNested(object str)
{
    var obj = JsonConvert.DeserializeObject<object>((string)str);
 
    var settings = new JsonSerializerSettings
    {
        ContractResolver = new DefaultContractResolver
        {
            NamingStrategy = new SnakeCaseNamingStrategy { ProcessDictionaryKeys = true }
        },
        Formatting = Formatting.Indented
    };
    var json = JsonConvert.SerializeObject(obj, settings);
    return json;
}