how can i add the sendgrid webhook event Json response in a firebase cloud firestore using node.js

As you will read in the Sendgrid documentation:

SendGrid's Event Webhook will notify a URL of your choice via HTTP POST with information about events that occur as SendGrid processes your email

To implement the HTTP endpoint in your Firebase Project, you will implement an HTTPS Cloud Function that will be called by the Sendgrid webhook through an HTTPS POST request.

Each call from the Sendgrid webhook will concern a specific event and you will be able, in your Cloud Function, to get the value of the event (processed, delivered, etc...).

Now, you need in your Cloud Function to be able to link a specific event with a specific email that was previously sent through your Cloud Function. For that you should use custom arguments.

More precisely, you would add to your msg object (that you pass to the send() method) a unique identifier. A classical value is a Firestore document ID, like event.params.officeId but could be any other unique ID that you generate in you Cloud Function.

Example of implementation

In your Cloud Function that sends the email, pass the officeId in a custom_args object, as shown below:

 exports.sentMail = functions.firestore
  .document("/Offices/{officeId}")
  .onCreate((documentSnapshot,event) => {

    const documentData = documentSnapshot.data();

    const officeId = event.params.officeId;

    const msg = {
          to: "[email protected]",
          from: "[email protected]",
          text: "hello from this side",
          templateId: "d-8ecfa59aa9d2434eb8b7d47d58b4f2cf",
          substitutionWrappers: ["{{", "}}"],
          substitutions: {
            name: documentData.name
          },
          custom_args: {
             "officeId": officeId
          }
    };
    
    return sgMail.send(msg)
      .then(() => {
         console.log("payment mail sent success"));
         return null;
      })
      .catch(err => {
         console.log(err)
         return null;
      });
  });

Note that you get the data of the newly created document (the one which triggers the Cloud Function) through documentSnapshot.data(): you don't need to query for the same document in your Cloud Function.

Then, create a simple HTTPS Cloud Function, as follows:

exports.sendgridWebhook = functions.https.onRequest((req, res) => {
    const body = req.body; //body is an array of JavaScript objects

    const promises = [];

    body.forEach(elem => {

        const event = elem.event;
        const eventTimestamp = elem.timestamp;
        const officeId = elem.officeId;

        const updateObj = {};
        updateObj[event] = true;
        updateObj[event + 'Timestamp'] = eventTimestamp;

        promises.push(admin.firestore().collection('Offices').doc(officeId).update(updateObj));

    });

    return Promise.all(promises)
        .then(() => {
            return res.status(200).end();
        })

})

Deploy it and grab its URL as shown in the terminal: it should be like https://us-central1-<your-project-id>.cloudfunctions.net/sendgridWebhook.

Note that here I use admin.firestore().collection('Offices').... You may use const db = newProject.firestore(); ... db.collection('Offices')...

Also note that the body of the HTTPS POST request sent by the Sendgrid webhook contains an array of JavaScript objects, therefore we will use Promise.all() to treat these different objects, i.e. write to the Firestore document with officeId the different events.

Then you need to set-up the Webhook in the Sendgrid platform, in the "Mail Settings/Event Notification" section, as explained in the doc and as shown below.