message": "Webhook call failed. Error: UNAVAILABLE, State: URL_UNREACHABLE, Reason: UNREACHABLE_5xx, HTTP status code: 500." in dialogflow fulfillment - google-cloud-functions

Question

I am trying to send email using dialogflow intents from my gmail. But it throws the same error every time and I am unable to understand the issue behind this. The same thing stand alone from my code is able to send emaail to various email addresses. So i guess the code works just fine . Please have a look at my code .
'use strict';
const functions = require('firebase-functions');
const {WebhookClient} = require('dialogflow-fulfillment');
const {Card, Suggestion} = require('dialogflow-fulfillment');
const nodemailer = require("nodemailer");
const admin = require("firebase-admin");
const axios = require("axios");
admin.initializeApp({
credential:admin.credential.applicationDefault(),
databaseUrl:'ws://***************/'
});
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 my agent!`);
}
function fallback(agent) {
agent.add(`I didn't understand`);
agent.add(`I'm sorry, can you try again?`);
}
function emailSend(){
const email= agent.parameters.email;
const name= agent.parameters.name;
const subject= agent.parameters.subject;
const message = agent.parameters.message;
}
const nodemailer = require('nodemailer');
var transporter = nodemailer.createTransport({
service: 'gmail',
auth: {
user: '*****#gmail.com',
pass: '***********'
}
});
var mailOptions = {
from: 'Mamuni',
to: 'email' ,
subject: 'subject' ,
text: 'message'
};
transporter.sendMail(mailOptions, function(error, info){
if (error) {
console.log(error);
} else {
console.log('Email sent: ' + info.response);
}
});
let intentMap = new Map();
intentMap.set('emailSend',emailSend);
intentMap.set('Default Welcome Intent', welcome);
intentMap.set('Default Fallback Intent', fallback);
agent.handleRequest(intentMap);
});

Answer 1

The error probably is indicative that your code is not reachable or probably not being served via a HTTPS endpoint. I suggest the following:
Is the code available over a publicly accessible endpoint?
If the above is yes, is it being served over a secure channel i.e. HTTPS?