public static string CreateSHA256Signature(string key, string message)
        {
            // Hex Decode the Secure Secret for use in using the HMACSHA256 hasher
            // hex decoding eliminates this source of error as it is independent of the character encoding
            // hex decoding is precise in converting to a byte array and is the preferred form for representing binary values as hex strings.
           var convertedHash = new byte[key.Length / 2];
            for (var i = 0; i < key.Length / 2; i++)
            {
                convertedHash[i] = (byte)int.Parse(key.Substring(i * 2, 2), System.Globalization.NumberStyles.HexNumber);
            }

            // Create secureHash on string
            var hexHash = "";
            using (var hasher = new HMACSHA256(convertedHash))
            {
                var hashValue = hasher.ComputeHash(Encoding.UTF8.GetBytes(message));
                hexHash = hashValue.Aggregate(hexHash, (current, b) => current + b.ToString("X2"));
            }
            return hexHash;
        }