getting conformancelevel error creating xml

I keep getting "Token Text in state Start would result in an invalid XML document. Make sure that the ConformanceLevel setting is set to ConformanceLevel.Fragment or ConformanceLevel.Auto if you want to write an XML fragment." Error when submitting this xml that I created - any Ideas? the xml output is
<TRANSACTION>
  <FUNCTION_TYPE>SECURITY</FUNCTION_TYPE>
  <COMMAND>REGISTER</COMMAND>
  <ENTRY_CODE>7663</ENTRY_CODE>
  <KEY>MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA9XUubjG7MFc5VarQw/ZPOS0flHAVI0BVNJHTMuuS2vv6ZHNcPjkymBJ8d9RVu7nBsPEOw5DixqFNLWRngXAsTL+UVAkqm9Ci2xU/GkSlbijfhe2xSp+8i8TK5mcjZLKEyG2Oux6aA6UftiYqLtmfzMyKhAvXyo0d1EYVQvPoJ0i8dOazlctunI//ThfZYR3hxeSlPYu5PoqLVGZvKFal2NVHbaBnso02wJgMqbfX6uM5zXpuLNKj8iGPbQmAzJOBy8mwbbZGx73elWei60xWMRyh85qCHSW2ylP/h6EjoqfvjAl/Y6BS5cjIHT4mz3rJqH0Y1QRwxQiBSXLYgBYDJwIDAQAB</KEY>
</TRANSACTION>

   var request = new XDocument();
            XmlWriterSettings settings = new XmlWriterSettings();
            settings.Indent = true;
            settings.NewLineChars = Environment.NewLine;
            settings.NewLineOnAttributes = true;
            settings.NewLineHandling = NewLineHandling.Replace;
            settings.NewLineOnAttributes = true;
            settings.ConformanceLevel = ConformanceLevel.Fragment;
            settings.CloseOutput = false;


            using (var writer = request.CreateWriter())
            {
               
                writer.WriteStartDocument();
                writer.WriteStartElement("TRANSACTION");
                writer.WriteElementString("FUNCTION_TYPE", "SECURITY");
                writer.WriteElementString("COMMAND", "REGISTER");
                writer.WriteElementString("ENTRY_CODE", entryCode);
                writer.WriteElementString("KEY", publicEncodedString);
                writer.WriteEndElement();
                writer.WriteEndDocument();
                writer.Flush();
            }

            // transmit to Point Solution and interrogate the response
            var responseXml = Send(address, port, request);

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