QuickBooks oAuth2 Get Tokens With Auth Code (NodeJs)

Question

I am having trouble setting up my function to get my auth tokens from quickbooks using the auth code.

cors(req, res, async () => {
const clientId = functions.config().quickbooks.client_id;
const clientSecret = functions.config().quickbooks.client_secret;
const redirectUri = functions.config().quickbooks.redirect_uri;

const basicAuth = require('btoa')(clientId + ':' + clientSecret)

const { code } = req.body;

if (!code) {
  return res.status(400).send({ error: 'Authorization code is required' });
}

// Prepare the request body (URL encoded)
const requestBody = new URLSearchParams({
  grant_type: 'authorization_code',
  code: code,
  redirect_uri: redirectUri,
}).toString();


try {
  const response = await fetch('https://oauth.platform.intuit.com/oauth2/v1/tokens/bearer', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/x-www-form-urlencoded',
      'Authorization': `Basic ${basicAuth}`,
      'Accept': 'application/json',
    },
    body: requestBody,
  });

  // Check if response is OK, else log the error
  if (!response.ok) {
    const errorDetails = await response.text();  // Capture non-JSON response
    console.error("QuickBooks API Error:", errorDetails);
    return res.status(500).send({ error: 'Error authenticating with QuickBooks', details: errorDetails });
  }

  const data = await response.json();
  return res.status(200).send({ success: true, data: data });
} catch (error) {
  console.error("Error in exchangeAuthCodeForTokens function:", error.message);
  return res.status(500).send({ error: error.message });
}
});

I am always getting status 500 (Internal Server Error)

I have console-logged all variables, and they match, with no other errors found.

What could I be doing here that could cause the issues at hand? Any help would be great, thanks!