google oauth2 suddenly failing with Malformed auth code error

I am trying to write a javascript file that uses the youtube v3 api.

i created a google cloud project, enable youtube api, and go through the credentials creation process, which at the end leads me to download a json file with my client id etc...

The resulting 'client_secret.json' file looks like this:

{
"web": {
"client_id": "aaaaaa",
"project_id": "aaaa",
"auth_uri": "aaaa",
"token_uri": "aaaa": "https://www.googleapis.com/oauth2/v1/certs",
"client_secret": "aaaaa",
"redirect_uris": [
"http://localhost:3030/"
]
}
}

I have a file titled 'attempt.js' :

const { google } = require('googleapis');
const readline = require('readline');
const fs = require('fs');
// YouTube API credentials
var CLIENT_ID = '';
var CLIENT_SECRET = '';
var REDIRECT_URL = '';
var SCOPES = ['https://www.googleapis.com/auth/youtube.readonly'];
main()
async function main() {
console.log('set auth vars from json file')
await getAuthVars()
async function getAuthVars() {
return new Promise(async function (resolve, reject) {
fs.readFile('client_secret.json', function processClientSecrets(err, content) {
if (err) {
console.log('Error loading client secret file: ' + err);
return;
}
content = JSON.parse(content)
console.log('content=', content)
CLIENT_SECRET = content.web.client_secret;
CLIENT_ID = content.web.client_id;
REDIRECT_URL = content.web.redirect_uris[0];
resolve()
});
})
}
console.log('begin auth flow')
beginAuthFlow()
async function beginAuthFlow() {
// Create an OAuth2 client
const oAuth2Client = new google.auth.OAuth2(
CLIENT_ID,
CLIENT_SECRET,
REDIRECT_URL
);
// Generate the authentication URL
const authUrl = oAuth2Client.generateAuthUrl({
access_type: 'offline',
scope: SCOPES
});
// Create an interface for reading user input
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
// Ask the user to visit the authentication URL and provide the authorization code
console.log('Authorize this app by visiting the following URL:');
console.log(authUrl);
rl.question('Enter the authorization code: ', (code) => {
rl.close();
// Exchange authorization code for access token
oAuth2Client.getToken(code, (err, token) => {
if (err) {
console.error('Error retrieving access token:', err);
return;
}
// Set the access token for future requests
oAuth2Client.setCredentials(token);
// Create a YouTube service client
const youtube = google.youtube({
version: 'v3',
auth: oAuth2Client
});
// Retrieve details about the authenticated user's YouTube account
youtube.channels.list(
{
mine: true,
part: 'snippet,contentDetails,statistics'
},
(err, res) => {
if (err) {
console.error('Error retrieving channel details:', err);
return;
}
// Display the channel information
const channel = res.data.items[0];
console.log('Channel ID:', channel.id);
console.log('Channel Title:', channel.snippet.title);
console.log('Subscriber Count:', channel.statistics.subscriberCount);
console.log('View Count:', channel.statistics.viewCount);
console.log('Video Count:', channel.statistics.videoCount);
}
);
});
});
}
}

When I run this file with node attempt.js it creates the URL correctly, which I think is good because it means my auth stuff is working:

begin auth flow
Authorize this app by visiting the following URL:
https://accounts.google.com/o/oauth2/v2/auth?access_type=offline&scope=aaaaaa&response_type=code&client_id=aaaaaaa&redirect_uri=http%3A%2F%2Flocalhost%3A3030%2F
Enter the authorization code: 

I go to the URL, sign into a youtube account, and it redirects to a url like so:

http://localhost:3031/?code=4%2F0aaaaaa

So I copy everything after the 'code=' string, so the following text is in my copy clipboard: 4%2F0aaaaaa

I paste that in my terminal window and hit enter, which gives me this error:

Error retrieving access token: GaxiosError: invalid_grant
data: {
error: 'invalid_grant',
error_description: 'Malformed auth code.'
},

What am i doing wrong?

code that i copied from browser url had to be decoded in script:

oAuth2Client.getToken(decodeURIComponent(code), (err, token) => {

works