Firebase SendEmail function works only on 3rd click - node.js

Question

I am using firebase SendEmail function in my React app (for Contact Form). After all deployment, when I test it through my Contact Form, it doesn't work upon "Submit" request. But it works only when I click immediate after getting second failer message after timeouts. If I repeat new Submit later, it again doesn't work but only with 3rd click.
Here is the error message:
Access to fetch at 'https://us-central1-myapp.cloudfunctions.net/sendEmail' from origin 'https://www.mydomain.co' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.
And then "Failed to load resource: net::ERR_FAILED".
When it works, no error message there of course.
Here is my code (C:...\root\functions\index.js):
//import needed modules
const functions = require('firebase-functions');
const nodemailer = require('nodemailer');
//when this cloud function is already deployed, change the origin to 'https://your-deployed-app-url
const cors = require('cors')({ origin: 'https://www.mydomain.co' });
//create and config transporter
let transporter = nodemailer.createTransport({
host: 'mail.mydomain.co',
port: 465,
secure: true, // true for 465, false for other ports
auth: {
user: 'info#mydomain.co',
pass: '********'
},
});
//export the cloud function called `sendEmail`
exports.sendEmail = functions.https.onRequest((req, res) => {
//for testing purposes
console.log(
'from sendEmail function. The request object is:',
JSON.stringify(req.body)
);
//enable CORS using the `cors` express middleware.
cors(req, res, () => {
//get contact form data from the req and then assigned it to variables
const name = req.body.data.name;
const email = req.body.data.email;
const company = req.body.data.company;
const subject = req.body.data.subject;
const message = req.body.data.message;
//config the email message
const mailOptions = {
from: email,
to: `info#mydomain.com`,
subject: subject,
text: `Name: ${name}, Company: ${company} Message: ${message}`,
};
//call the built in `sendMail` function and return different responses upon success and
failure
return transporter.sendMail(mailOptions, (error, info) => {
if (error) {
return res.status(500).send({
data: {
status: 500,
message: error.toString(),
},
});
}
return res.status(200).send({
data: {
status: 200,
message: 'sent',
},
});
});
});
});
Also, although Postman sends emails from localhost app, it absolutely doesn't send email when the app deployed (when used the function's online url: https://us-central1-myapp.cloudfunctions.net/sendEmail).
Any ideas about this issue, please?