How do I use AddNodesToNCM VIA REST API

I have only been using solarwinds for a short time and I am not a great programmer, but I have successfully added new nodes into solarwinds, I'm feeling pretty confident about adding pollers and discovering / adding interfaces.

However I need some help adding a node into NCM.

I am trying to use the following request to add Node ID 11985 into NCM.

<?php

$curl = curl_init();

curl_setopt_array($curl, array(

  CURLOPT_PORT => "17778",

  CURLOPT_URL => "https://SERVERIP:17778/SolarWinds/InformationService/v3/Json/Invoke/Cirrus.Nodes.AddNodeToNCM",

  CURLOPT_RETURNTRANSFER => true,

  CURLOPT_ENCODING => "",

  CURLOPT_MAXREDIRS => 10,

  CURLOPT_TIMEOUT => 30,

  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,

  CURLOPT_CUSTOMREQUEST => "POST",

  CURLOPT_POSTFIELDS => "\"11985\"",

  CURLOPT_HTTPHEADER => array(

    "authorization: Basic REMOVED",

    "content-type: application/json"

  ),

));

$response = curl_exec($curl);

$err = curl_error($curl);

curl_close($curl);

if ($err) {

  echo "cURL Error #:" . $err;

} else {

  echo $response;

}

?>

This was processed from the Insomnia REST client.

I receive the following error:

"Expecting state 'Element'.. Encountered 'Text'  with name '', namespace ''. "

Please help me understand how to use this API method.

Thanks,

Matt