"Unhandled rejection" message when trying to display data from Firestore Database in Dialogflow payload

I'm new at this & I've read numerous similar articles but none worked for me. I really need close assistance. I'm developing a chatbot using Dialogflow & using the Fulfillment Inline Editor. I wanted an intent where when user enters "Read db" the readDB() function will be triggered and the data from database will be stored in a custom payload. Here is my code:

'use strict';
 
const functions = require('firebase-functions');
const admin = require('firebase-admin');
const {WebhookClient} = require('dialogflow-fulfillment');
const {Card, Suggestion} = require('dialogflow-fulfillment');
const {Payload} = require("dialogflow-fulfillment");

const serviceAccount = {
  "type": "service_account",
  "project_id": xxx,
  "private_key_id": xxx,
  "private_key": xxx,
  "client_email": xxx,
  "client_id": xxx,
  "auth_uri": xxx,
  "token_uri": xxx,
  "auth_provider_x509_cert_url": xxx
  "client_x509_cert_url": xxx
};

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
  databaseURL: "https://repro-ljcq.firebaseapp.com/"
});
const db = admin.firestore();
db.settings({timestampsInSnapshots: true});
 
process.env.DEBUG = 'dialogflow:debug'; 
 
exports.dialogflowFirebaseFulfillment = functions.https.onRequest((request, response) => {
  const agent = new WebhookClient({ request, response });
    
  function displayDB(){
    return admin.firestore().collection('ICR').doc(sessionID).get()
      .then(doc => {
      data = doc.data();
      const payload = {
          "accordion": {
            "title": "Individual Client Record",
            "group": data.groups,
            "age":  data.age,
            "birthdate": data.birthdate,
            "name": data.fullname,
            "phonenumber": data.contactnumber,
            "address": data.address,
            "sex": data.sex,
            "civilstatus": data.civilstatus
          }
        };
        agent.add(new Payload(agent.UNSPECIFIED, payload, {rawPayload: true, sendAsMessage: true}));
    });
  }

  let intentMap = new Map();
  intentMap.set('ReadDB', displayDB);
  agent.handleRequest(intentMap);
});

This is what my Database Structure looks like.

In my client-side app, it works fine when I use dummy values. This is what it was supposed to look like.

I can view the data in the logs, but receive "unhandled rejection" error message whenever I try to put it in the payload. Here is the logs:

I don't know whether this is from the wrong execution of the payloads or because of the timeout (retrieving data from firebase takes longer than 5s that it reaches Dialogflow timeout)

I really need help :/

Found the answer! Had to restructure the promise into something like this and upgrade my dependencies.

index.js

return admin.firestore().collection('ICR').doc(sessionID).get().then((doc) => {
      const data = doc.data();
      console.log(data);
      return data;
    }).then(data => {
      if (data){
        payload = {
          "accordion": {
            "filename": sessionID,
            "title": "Individual Client Record",
            "name": data.fullname,
            "age":  data.age + " years old",
            "sex": data.gender,
            "civilstatus": data.civilstatus,
            "birthdate": data.birthdate,
            "phonenumber": data.phonenumber,
            "group": data.group,
            "address": data.address
          }
        };
        agent.add(new Payload(agent.UNSPECIFIED, payload, {rawPayload: true, sendAsMessage: true}));
      } else {
        //do something
      }
    }).catch(err => {
      console.log(`Error fetching to Firestore.`);
    });

package.json

{
  "name": "dialogflowFirebaseFulfillment",
  "description": "This is the default fulfillment for a Dialogflow agents using Cloud Functions for Firebase",
  "version": "0.0.1",
  "private": true,
  "license": "Apache Version 2.0",
  "author": "Google Inc.",
  "engines": {
    "node": "10"
  },
  "scripts": {
    "start": "firebase serve --only functions:dialogflowFirebaseFulfillment",
    "deploy": "firebase deploy --only functions:dialogflowFirebaseFulfillment"
  },
  "dependencies": {
    "actions-on-google": "^2.5.0",
    "firebase-admin": "^7.0.0",
    "firebase-functions": "^2.2.0",
    "dialogflow": "^0.8.0",
    "dialogflow-fulfillment": "^0.6.1"
  }
}

Code highly influenced from mikkipastel.