I am trying to Access the private Poloniex trading API in Unity C# but am getting the error "invalid command"

Question

I am trying to Access the private Poloniex trading API in Unity C# but am getting the error "invalid command" I have my API Key and Secret authorized on Poloniex for the Trading API but can't seem to get access with my current code:

 using System.Collections;
    using System.Collections.Generic;
    using UnityEngine;
    using System;
    using System.Security.Cryptography;


    public class PolonScript : MonoBehaviour {


        public TextMesh OutputText;

        const string _apiKey = "---Key---";
        const string _apiSecret = "---secret---";


        void Start () {

            string nonce = DateTime.Now.ToString("HHmmss");

            string myParam = "command=returnBalances&nonce=" + nonce;


            const string WEBSERVICE_URL = "https://poloniex.com/tradingApi";
            try
            {
            var webRequest = System.Net.WebRequest.Create(WEBSERVICE_URL);
                if (webRequest != null)
                {
                    webRequest.Method = "POST";
                    webRequest.Timeout = 12000;
                webRequest.ContentType = "application/x-www-form-urlencoded";
                    webRequest.Headers.Add("Key", _apiKey);
                    webRequest.Headers.Add("Sign", genHMAC(myParam));
                    webRequest.Headers.Add("command", "returnBalances");
                    webRequest.Headers.Add("nonce", nonce.ToString());


    using (System.IO.Stream s = webRequest.GetResponse().GetResponseStream())
                    {
                        using (System.IO.StreamReader sr = new System.IO.StreamReader(s))
                        {
                            var jsonResponse = sr.ReadToEnd();
                            OutputText.text = jsonResponse.ToString();
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                OutputText.text = ex.ToString();
            }




        } //end-of-start()

Here is my current signing method which I am quite sure has a mistake (Human error) within, am I doing something wrong obliviously here?

        private string genHMAC(string message)
        {
            byte [] APISecret_Bytes = System.Text.Encoding.UTF8.GetBytes(_apiSecret);
            byte [] MESSAGE_Bytes = System.Text.Encoding.UTF8.GetBytes(message);

            var hmac = new HMACSHA512(APISecret_Bytes);
            var hashmessage = hmac.ComputeHash(MESSAGE_Bytes);

            var sign = BitConverter.ToString(hashmessage).Replace("-", "").ToLower();
            return sign;
        }




    }

Answer 1

Poloniex Command should not be sent in the header, you should send it as a POST parameter, that's why it's responding "invalid command". Take a look at this answer to see how you send POST parameters in c#:How to add parameters into a WebRequest?

Here's an example of how your Start method should look like:

void Start()
{

    string nonce = DateTime.Now.ToString("HHmmss");

    string myParam = "command=returnBalances&nonce=" + nonce;


    const string WEBSERVICE_URL = "https://poloniex.com/tradingApi";
    try
    {
        var webRequest = System.Net.WebRequest.Create(WEBSERVICE_URL);
        if (webRequest != null)
        {
            webRequest.Method = "POST";
            webRequest.Timeout = 12000;
            webRequest.ContentType = "application/x-www-form-urlencoded";
            webRequest.Headers.Add("Key", _apiKey);
            webRequest.Headers.Add("Sign", genHMAC(myParam));

            byte[] dataStream = Encoding.UTF8.GetBytes($"command=returnBalances&nonce={nonce.ToString()}");
            webRequest.ContentLength = dataStream.Length;

            Stream newStream = webRequest.GetRequestStream();
            newStream.Write(dataStream, 0, dataStream.Length);
            newStream.Close();

            using (System.IO.Stream s = webRequest.GetResponse().GetResponseStream())
            {
                using (System.IO.StreamReader sr = new System.IO.StreamReader(s))
                {
                    var jsonResponse = sr.ReadToEnd();
                    OutputText.text = jsonResponse.ToString();
                }
            }
        }
    }
    catch (Exception ex)
    {
        OutputText.text = ex.ToString();
    }
}