First of all, your bot access token has the right to read posts and attachments under a team/chat/conversation the bot is a member of.

In your case, I don't see the code nor the environment so it's hard for me to tell what could be wrong. This is how I could successfully download a binary file attachment in my bot using Node JS.

const url = require('url')

try{

  var attachmentUri = "https://dl.mvp.ringcentral.com/file/NNN"

  var accessToken = "Valid-AccessToken"

  download(attachmentUri, accessToken, (err, content) => {

     console.log("Done")

  })

}catch(e){

  console.log(e)

}

var https = require('https');

const download = function(attachmentUri, token, cb) {

  var file = fs.createWriteStream("testing.png");

  var u = url.parse(attachmentUri);

  var options = {

    host: u.host,

    path: u.pathname,

    method: "GET",

    headers: {

        Authorization: `Bearer ${token}`

      }

    }



  const req = https.request(options, res => {

    var chunks = [];

    res.setEncoding('binary');

    res.on('data', (chunk) => {

      chunks += chunk;

    }).on('end', () => {

      file.write(chunks, 'binary');

      file.on('finish', () => {

        console.log('File Saved !');

    });

    res.pipe(file);

    })

  })

  req.on('error', error => {

    console.error(error)

  })

  req.end()

}

If you believe that your code is correct and you still receive the error, I recommend to submit a dev support ticket so you can provide more details for the investigation.

Some code for your reference: https://github.com/tylerlong/rc-team-messaging-attachment-download/blob/main/src/demo.ts

It works for me.