My application uses the Zoom API with OAuth.
The process is well put in the zoom developer docs and I followed them
I created a zoom app in the developer's account and got the clientID and clientSecret.
First we need to get the Authorization code from "https://zoom.us/oauth/authorize". With this code we can get the access token from "https://zoom.us/oauth/token". Pretty straight forward. I tried it on Postman and all the APIs work.
My JS code below doesn't work and keeps failing to do this task.

const express = require('express');
const axios = require('axios');
let token = null;

const app = express();

const clientId = 'ADqR4l7KTfMmXXXXXXXX';
const clientSecret = 'mhVytefIFS4fSqQ3XXXXXXXXXX';
const redirectURL = 'http://localhost:3000/oauth-callback'

app.get('/', (req, res) => {
  res.redirect(`https://zoom.us/oauth/authorize?response_type=code&client_id=${clientId}&redirect_uri=${redirectURL}`);
});

app.get('/oauth-callback', (req, res) => {
  const body = {
    client_id: clientId,
    client_secret: clientSecret,
    code: req.query.code
  };
  const opts = { headers: { accept: 'application/json' } };
  axios.post(`https://zoom.us/oauth/token`, body, opts).
    then(res => res.data['access_token']).
    then(_token => {
      console.log('My token:', token);
      token = _token;
      res.json({ ok: 1 });
    }).
    catch(err => res.status(500).json({ message: err.message }));
});

app.listen(3000);
console.log('App listening on port 3000');

zoom dev acct:

zoom dev account

Error message:

Error message

How can I get the access token? Please help me find my errors in the code.