Dialogflow Webhook Firestore returns webhook failed status code 04, How to fix and get output from the firestore?

Question

I am trying to integrate dialogflow with firestore but I can't get the required output. Diagnostic Info provides the below error. I need to get the response from the firestore according to the given input from the agent that's the basic requirement but I get this error while integrating.

 {
  "responseId": "a6a119a8-c406-4af2-aab0-b6863fb091a4-59c3eb0f",
  "queryResult": {
    "queryText": "15APC2375",
    "parameters": {
      "regno": "15APC2375"
    },
    "allRequiredParamsPresent": true,
    "intent": {
      "name": "projects/cis-bot-yhrvph/agent/intents/e3b1292b-89b1-48b7-b4b4-805a63d08168",
      "displayName": "request-results"
    },
    "intentDetectionConfidence": 0.3,
    "diagnosticInfo": {
      "webhook_latency_ms": 4892
    },
    "languageCode": "en"
  },
  "webhookStatus": {
    "code": 4,
    "message": "Webhook call failed. Error: DEADLINE_EXCEEDED."
  }
}

My Package.json includes the below code.

{
  "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": {
    "firebase": "^7.13.2",
    "actions-on-google": "^2.2.0",
    "firebase-admin": "^5.13.1",
    "firebase-functions": "^2.0.2",
    "dialogflow": "^0.6.0",
    "dialogflow-fulfillment": "^0.5.0"
  }
}

As well as index.js includes the below code.

'use strict';
 
const firebase = require('firebase');

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

admin.initializeApp();
const db = admin.firestore();


process.env.DEBUG = 'dialogflow:debug'; // enables lib debugging statements
 
exports.dialogflowFirebaseFulfillment = functions.https.onRequest((request, response) => {
  const agent = new WebhookClient({ request, response });
  console.log('Dialogflow Request headers: ' + JSON.stringify(request.headers));
  console.log('Dialogflow Request body: ' + JSON.stringify(request.body));
 
  function welcome(agent) {
    agent.add(`Welcome to CIS BOT!`);
  }
 
  function fallback(agent) {
    agent.add(`Please Contact the Front Desk for more information`);
  }
  
  function getResults(agent){
    const regno=agent.parameters.regno;
    const dialogflowAgentDoc = db.collection('results').where("reg_id","==",'15APC2375')
    .get()
    .then((querySnapshot) => {
        querySnapshot.forEach((doc) => {
            // doc.data() is never undefined for query doc snapshots
            agent.add(doc.data().grade);
        });
      }).catch(() => {
        agent.add('Error reading entry from the Firestore database.');
        agent.add('Please add a entry to the database first by saying, "Write <your phrase> to the database"');
      });
  }
  
let intentMap = new Map();
  intentMap.set('Default Welcome Intent', welcome);
  intentMap.set('Default Fallback Intent', fallback);
  intentMap.set('request-results', getResults);
  // intentMap.set('your intent name here', googleAssistantHandler);
  agent.handleRequest(intentMap);
});