How to create WebPhone with javascript SDK

This is the modified version of the example code on Github:

var appKey = '...';
var appSecret = '...';
var appName = '...';
var appVersion = '...';

var sdk = new RingCentral.SDK({
    appKey: appKey,
    appSecret: appSecret,
    appName: appName,
    appVersion: appVersion,
    server: RingCentral.SDK.server.production // or .sandbox
});

var remoteVideoElement =  document.getElementById('remoteVideo');
var localVideoElement  = document.getElementById('localVideo');

var platform = sdk.platform();
platform.auth().setData(tokens)
if (platform.loggedIn()){
    platform.post('/client-info/sip-provision', {
          sipInfo: [{transport: 'WSS'}]
    })
    .then(function(res) { // Doing nested then because we need loginResponse in a simple way
        return new RingCentral.WebPhone(res.json(), { // optional
              appKey: appKey,
              appName: appName,
              appVersion: appVersion,
              uuid: loginResponse.json().endpoint_id,
              logLevel: 1, // error 0, warn 1, log: 2, debug: 3
              audioHelper: {
                  enabled: true, // enables audio feedback when web phone is ringing or making a call
                  incoming: 'path-to-audio/incoming.ogg', // path to audio file for incoming call
                  outgoing: 'path-to-audio/outgoing.ogg' // path to aduotfile for outgoing call
              },
              media:{
                  remote: remoteVideoElement,
                  local: localVideoElement
              },
              //to enable QoS Analytics Feature
              enableQos:true
          });

    })
    .then(function(webPhone){

        // YOUR CODE HERE
        
    })
}