Next.js API Route Works on Local Dev But Not Production (MailChimp API)

I'm working on a next.js project, and when running my project locally, I'm able to insert an email into a form and successfully POST it to MailChimp via their API. In production, the same code doesn't work, but I've confirmed that production has:

• Access to and correct MailChimp API key Next API route
• Api route {URL}/subscribe returns 200

The issue seems to be after the API route is called and the subsequent API call happens. I'm lost and would love your insights.

pages/api/subscribe.js

const axios = require('axios');

const LIST_ID = 'b29d6f1e61'; // MailChimp Audience
const key = `Basic ${Buffer.from(`apikey:${process.env.MAILCHIMP_API_KEY}`).toString('base64')}`;


const subscribe = ( email ) => {
axios({
    method: 'POST',
    url: `https://us18.api.mailchimp.com/3.0/lists/${LIST_ID}/members/`,
    headers: {Authorization: key},
    data: { email_address: `${email}`, status: "subscribed" } })
    .then(response => {
        console.log(response);
        return response
    }).then(data => {
        console.log('Data Rec\'d:', data);
    }).catch(error => {
        console.log('Subscribe error:', error);
        // reject('Something went wrong')
    });

};

module.exports = async (req, res) => {
    if (req.method === 'POST') {
        res.setHeader('Content-Type', 'application/json');
        res.statusCode = 200;
        res.send(req);
        await subscribe(req.body);
        res.end()
    } else {
        res.setHeader('Content-Type', 'application/json');
        res.statusCode = 200;
        res.end(JSON.stringify({name: 'GET received'}))
    }
};