获取access_token时，Etsy API说UnAuthorized（401）

Question

我正在关注this问题以连接Etsy API，并编写了以下代码：

class Etsy
    {
        private const string ACCESS_TOKEN = "jagbkdwqii82lhiaj2pqcujd ";
        private const string SECRET = "is1bztdh2k";
        private const string BASE_URL = "https://openapi.etsy.com/v2";
        private string token = "";
        public Etsy()
        {
            String f = "";
            try
            {

                var request_token_url = BASE_URL + "/oauth/request_token";
                var oauth = new Manager();
                oauth["consumer_key"] = ACCESS_TOKEN;
                oauth["consumer_secret"] = SECRET;
                oauth.AcquireRequestToken(request_token_url, "POST");
                f = "REQUIRED TOKENS = " + oauth["token"].ToString();
                token = f;
            }
            catch (Exception ex)
            {
                Console.WriteLine("Exception: "+ex.Message);
                token = "Exception :\n"+ex.Message;
            }

        }
        public string show()
        {
            return token;
        }
    }

当我运行此代码时，它会一直出现Unauthorized(401)错误。我使用相同的凭据到Etsy Python Library然后它工作正常。我在哪里做错了？

更新

我进一步调试，发现它发送了以下标题：

HEADER:- OAuth oauth_callback="oob", oauth_consumer_key="jagbkdwqii82lhiaj2pqcujd", oauth_nonce="150z8543", oauth_signature="4QGkvgBiF%2BQpOYNcNNwWNIIrhJo%3D", oauth_signature_method="HMAC-SHA1", oauth_timestamp="1431409362", oauth_version="1.0"

缺少什么？