Pwa push error: what's going on with WebPushError,? - Codes Helper

name: "WebPushError",
  message: "Received unexpected response code",
  statusCode: 400,
  headers:
   { "content-type": "text/html; charset=UTF-8",
     date: "Fri, 24 Aug 2018 11:16:39 GMT",
     expires: "Fri, 24 Aug 2018 11:16:39 GMT",
     "cache-control": "private, max-age=0",
     "x-content-type-options": "nosniff",
     "x-frame-options": "SAMEORIGIN",
     "x-xss-protection": "1; mode=block",
     server: "GSE",
     "alt-svc": "quic=":443"; ma=2592000; v="44,43,39,35"",
     "accept-ranges": "none",
     vary: "Accept-Encoding",
     connection: "close" },
  body: "<HTML>\n<HEAD>\n<TITLE>UnauthorizedRegistration</TITLE>\n</HEAD>\n<BODY BGCOLOR="-sharpFFFFFF" TEXT="-sharp000000">\n<H1>UnauthorizedRegistration</H1>\n<H2>Error 400</H2>\n</BODY>\n</HTML>\n",
  endpoint: "https://fcm.googleapis.com/fcm/send/cMYLTEcm8xg:APA91bGz2y5mBVOUTi4T57Lbcq_re9IMHdnuq7tVXPfQ0IHuGtKv5Y_HNRAmglqjsvFNLisTvjRqRlmG3oi5Fu_lEnUp3nB9inN2xKRs_Wh92hZA0X_70P7h5BnhmPG15ZyrjIKMbpCg" 
}

Source
server.js

app.post("/register", function(req, res) {
    var endpoint = req.body.endpoint
    // var key = req.body.key 
    // var authSecret = req.body.authSecret
    // console.log(saveSubscriptionToDatabase)
    // //
    // saveRegistrationDetails(endpoint, key, authSecret)
    // console.log(11)
    const pushSubscription = {
      endpoint: req.body.endpoint,
      keys: {
        auth: req.body.authSecret,
        p256dh: req.body.key
      }
    }
    var body = "thank u for registering"
    var iconUrl = "http://localhost:3001/icon.png"
    console.log(pushSubscription)
    //
    webpush.sendNotification(pushSubscription,
      new Buffer(JSON.stringify({
          msg: body,
          url: "http://localhost:3001/pwa",
          icon: iconUrl
      }), "utf8")
    ).then( response => {
        res.sendStatus(201)
    }).catch(err => {
        console.log(err)
    })
})

 if("serviceWorker" in navigator) {
            navigator.serviceWorker.register("/sw.js")
            .then(function(registration) {
                return registration.pushManager.getSubscription()    // 
                    .then( subscription => {
                        if(subscription) return null
                        return registration.pushManager.subscribe({     
                            userVisibleOnly: true,
                            applicationServerKey: urlBase64ToUint8Array(vapidPublicKey)
                        })
                        .then( subscription => {   
                            console.log(subscription)
                            var rawKey = subscription.getKey ? subscription.getKey("p256dh") : ""
                            var key = rawKey ? btoa(String.fromCharCode.apply(null, new Uint8Array(rawKey))) : ""
                            var rawAuthSecret = subscription.getKey ? subscription.getKey("auth") : ""
                            var authSecret = rawAuthSecret ? btoa(String.fromCharCode.apply(null, new Uint8Array(rawAuthSecret))) : ""
                            //
                            return fetch("/register", {
                                method: "post",
                                headers: new Headers({
                                    "content-type": "application/json"
                                }),
                                body: JSON.stringify({
                                    endpoint: subscription.endpoint,
                                    key: key,
                                    authSecret: authSecret
                                })
                            }) 
                        })
                        .catch( err => {
                            console.log("",err)
                            // console.log("!")
                        })
                    }) 
            })
            .catch(function(err) {
                console.log("err", err)
            })
        }