Nodemailer sending emails but getting ERR_HTTP_HEADERS_SENT - node.js

Question

I don't why i'm getting this every time I try to use Nodemailer to send emails:
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent
to the client
at new NodeError (node:internal/errors:371:5)
at ServerResponse.setHeader (node:_http_outgoing:576:11)
the thing is it's working but i'm getting this error, by working I mean It sends the email.
The Code:
const sendEmail = async (email, subject, payload, template) => {
try {
// create reusable transporter object using the default SMTP transport
const transporter = nodemailer.createTransport({
service: "gmail",
auth: {
user: process.env.EMAIL_USERNAME,
pass: process.env.EMAIL_PASSWORD,
},
});
const options = () => {
return {
from: process.env.FROM_EMAIL,
to: email,
subject: subject,
html: template,
};
};
// Send email
transporter.sendMail(options(), (error, info) => {
if (error) {
return error;
} else {
return res.status(200).json({
success: true,
});
}
});
} catch (error) {
throw error;
}
};
router.post("/", async (req, res, next) => {
try {
if (!req.body.newsletterEmail) {
return next(createError(400, "Please enter your email"));
} else if (!req.body.newsletterEmail || !isEmail(req.body.newsletterEmail)) {
return next(createError(400, "Please enter a valid email address"));
}
const checkEmail = await SubscribedEmails.findOne({ newsletterEmail: req.body.newsletterEmail });
if (checkEmail) {
return next(createError(400, "Email is already subscribed"));
} else {
//create new user
const newSubscribedEmail = new SubscribedEmails ({
newsletterEmail: req.body.newsletterEmail,
});
//save user and respond
const SubscribedEmail = await newSubscribedEmail.save();
res.status(200).json({
message: "Successfully subscribed",
SubscribedEmail,
});
const link = `${process.env.CLIENT_URL}/`;
await sendEmail(
SubscribedEmail.newsletterEmail,
"Welcome to our newsletter!",
{
link: link,
},
`<div> <p>Hi,</p> <p>You are subscribed to our.</p> <p> Please click the link below to view more</p> <a href=${link}>GO</a> </div>`
);
return res.status(200).send(link);
}
} catch(err) {
next(err);
}
});

Answer 1

This is likely due to some quirks with using Gmail with Nodemailer. Review the docs here - https://nodemailer.com/usage/using-gmail/
and configure your Gmail account here -
https://myaccount.google.com/lesssecureapps
Finally, you may run into issues with Captcha. Configure here - https://accounts.google.com/DisplayUnlockCaptcha