Pwa message push report error?

wrote this code according to the tutorial:

app.post("/register", jsonParser, 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 = "/icon.png"

    //
    webpush.sendNotification(pushSubscription,
      JSON.stringify({
          msg: body,
          url: "http://localhost:3001/pwa",
          icon: iconUrl
      })
    ).then( response => {
        res.sendStatus(201)
    }).catch(err => {
        console.log(err)
    })
})
The main reason for

saveRegistrationDetails is that I don"t know where this method came from.

Pwa
Apr.28,2021
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