How to add a XML request on the body of Restsharp call

Question

I'm developing a software who call API and I have to send to this API a request on XML to get more data.

I have allready tried request.AddXmlBody(nextID) but it doesn't work, I have also tried request.AddParameter("text/xml", nextID, ParametreType.RequestBody ) and I get an error : XML exception, root element is missing.

    var client = new RestClient("https://xxxxxxxxxxxxx.xxx");

    client.Authenticator = new HttpBasicAuthenticator("xxxxx", "xxxx");          
    var request = new RestRequest("/xx/xxx/xx/xx/xxxxx", Method.GET);
    string nextID = "<?xml version=\"1.0\" encoding=\"UTF - 8\" ?>< ServiceRequest > < filters > < Criteria field = \"id\" operator= \"GREATER\" > 13782472 </ Criteria ></ filters ></ ServiceRequest > ";
    request.AddHeader("X-Requested-With", "RestSharp");
    request.AddParameter(nextID);
    IRestResponse response = client.Execute(request);

    var xml_text = response.Content;

    string xq1 = "//*[contains(text(),'XXX')]/..";

    XmlDocument xd = new XmlDocument();
    xd.LoadXml(xml_text); 

I want to add my string nextID to the body of my request to get the file I want.

Answer 1

Thank's to @jdweng, my extra space on my string was my mistake.

This code works :

string nextID = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><ServiceRequest> <filters> <Criteria field = \"id\" operator=\"GREATER\"> 13782472 </Criteria></filters></ServiceRequest>"; 
        request.AddHeader("X-Requested-With", "RestSharp");
        request.AddParameter("text/xml", nextID, ParameterType.RequestBody);