I'm getting an error message 'resplatform is not defined' while following the webhooks getting started guide

https://developers.ringcentral.com/guide/notifications/webhooks/quick-start

I'm following the guide for webhooks and under getting started theres an example. I can log in but when the program gets to resplatform.post I get an error message 'resplatform is not defined' I have @ringcentral/sdk in my package and I ran npm install ringcentral --save

Where is resplatform supposed to be defined? Has the devkit removed that function?

var http = require('http');
const RingCentral = require('@ringcentral/sdk').SDK

RINGCENTRAL_CLIENTID = '<ENTER CLIENT ID>'
RINGCENTRAL_CLIENTSECRET = '<ENTER CLIENT SECRET>'
RINGCENTRAL_SERVER = 'https://platform.devtest.ringcentral.com'

RINGCENTRAL_USERNAME = '<YOUR ACCOUNT PHONE NUMBER>'
RINGCENTRAL_PASSWORD = '<YOUR ACCOUNT PASSWORD>'
RINGCENTRAL_EXTENSION = '<YOUR EXTENSION, PROBABLY "101">'

DELIVERY_ADDRESS = '<https://xxxxxxxx.ngrok.io/webhook>'

PORT = 5000

var server = http.createServer(function(req, res) {
  if (req.method == 'POST') {
    if (req.url == "/webhook") {
      if (req.headers.hasOwnProperty("validation-token")) {
        res.setHeader('Validation-Token', req.headers['validation-token']);
        res.statusCode = 200;
        res.end();
      } else {
        var body = []
        req.on('data', function(chunk) {
          body.push(chunk);
        }).on('end', function() {
          body = Buffer.concat(body).toString();
          var jsonObj = JSON.parse(body)
          console.log(jsonObj.body);
        });
      }
    }
  } else {
    console.log("IGNORE OTHER METHODS")
  }
});
server.listen(PORT);

var rcsdk = new RingCentral({ server: RINGCENTRAL_SERVER, clientId: RINGCENTRAL_CLIENTID, clientSecret: RINGCENTRAL_CLIENTSECRET });

var platform = rcsdk.platform();
platform.login({ username: RINGCENTRAL_USERNAME, password: RINGCENTRAL_PASSWORD, extension: RINGCENTRAL_EXTENSION })

platform.on(platform.events.loginSuccess, function(e) {
  console.log("Login success")
  subscribe_for_notification()
});

async function subscribe_for_notification() {
  var params = {
    eventFilters: ['/restapi/v1.0/account/~/extension/~/message-store/instant?type=SMS'],
    deliveryMode: {
      transportType: "WebHook",
      address: DELIVERY_ADDRESS
    }
  }
  try {
    var resp = await resplatform.post('/restapi/v1.0/subscription', params)
    var jsonObj = await resp.json()
    console.log(jsonObj.id)
    console.log("Ready to receive incoming SMS via WebHook.")
  } catch (e) {
    console.error(e.message);
    throw e;
  }
}