Axios Error : Request Failed with status code 500 - More Details on error below (React and Node.js and Nodemailer)

Question

I am trying to submit data from a form on my page to a node.js api using axios but i get the following error.

Error: Request failed with status code 500
    at createError (createError.js:16:1)
    at settle (settle.js:17:1)
    at XMLHttpRequest.onloadend

This is my onSubmit function where I use axios

const formSubmit = (e) => {
    e.preventDefault();

    let data = {
        firstname: firstName,
        secondname: secondName,
        email: email,
        industry: industry,
        message: message,
        number: number,
        website: website
    }

    axios.post('/api/forma' , data)
    .then(res => {
        setSent(true)
    },resetForm()
    ).catch(error => {
        console.log(error)
    })

}

This is the node.js part of the api

app.post('/api/forma' , (req , res) => {
    let data = req.body
    let smtpTransport = nodemailer.createTransport({
        host: 'mail.privateemail.com',
        port: 993,
        secure: false,
        auth: {
            user:'[email protected]',
            pass: '88WRHMMmmm'
        }
    });

    let mailOptions = {
        from: data.email,
        to: 'hzdigitalagency.com',
        subject: `HZ Agency Customer -  ${data.firstname} `,
        html: 
        "<h1>Hello </h1> <ul> <li> <li> Hello <ul>"
          
        
    }

    smtpTransport.sendMail(mailOptions, (error , response) => {
        if(error) {
            res.send(error)
        }
        else {
            res.send("Success")
        }
    })

    smtpTransport.close();
})

I am kind of a beginner to this so would really appreciate any help , Thanks in advance !

And It also shows this error

POST http://localhost:3000/api/forma 500 (Internal Server Error)

My node.js backend is running on server 5000 and frontend on 3000