First of all, you will need to add a web app manifest from https://developers.google.com/web/fundamentals/web-app-manifest/file in our project and add the following to it:

{
  "gcm_sender_id": "103953800507"
}

It tells the browser that FCM is allowed to send the messages to this App. The 103953800507 value is hard-coded and must be the same in any of your App. The web app manifest is a simple JSON file and will contain the configuration metadata related to your project, such as the start URL of your App and App icon details.

We have created a manifest.json file in the root folder of the code and added the preceding content to it.