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I did not download the attachment, I only used the get request to get the messages from a specific chat.

In the messages list, for each message, I get an attachments key whose value is an array holding the data about the attachments in the message - the data being those 4 keys I listed in my question.

I can't find any information in the documentation about how/where to attach a valid access token to the contentUri, so if you could help me out with that, that would be good.

Here is how you can download attachment files. The sample code is in Node JS and using the RingCentral JS SDK. See the quick start sample code for instruction how to use the JS SDK.

const fs    = require('fs')
const https = require('https')
const url = require('url')
const RC = require('@ringcentral/sdk').SDK


var contentUri = "https://dl.mvp.ringcentral.com/file/2222653882378"
var fileName = "Screenshot 2023-04-04 at 10.07.47 AM.png"
get_attachment_file(contentUri, fileName)


async function get_attachment_file(contentUri, fileName){
  var u = url.parse(contentUri)
  var tokenObj = await platform.auth().data()
  var accessToken = tokenObj.access_token
  download(u.host, u.path, accessToken, fileName, function(){
    console.log(`${fileName} file is saved to the local machine.`)
  })
}

const download = function(domain, path, accessToken, dest, cb) {
  var file = fs.createWriteStream(dest);
  var options = {
          host: domain,
          path: path,
          method: "GET",
          headers: {
            Authorization: `Bearer ${accessToken}`
          }
      }
  const req = https.request(options, res => {
    res.pipe(file);
    file.on('finish', function() {
      file.close(cb);
    });
  })
  req.on('error', error => {
    console.error(error)
  })
  req.end()
}

When I use the script you provided, with a valid access_token, I get this error in the script: TypeError [ERR_INVALID_CHAR]: Invalid character in header content ["Authorization"]. Do you know what could be causing it? From my research, it probably means that the server is not recognizing token as valid.

How do you get the access token? Do you use the platform exactly as I showed?

The access_token problem is resolved, I had a typo.

But, now I have another problem: while I am able to get the image via Postman, adjusting the Node script you shared above in order to download the blob via client, I get this error:
Access to fetch at 'https://dl.mvp.ringcentral.com/file/2222669840394' from origin 'http://localhost:3000' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

I got the same error when trying to make a get request from our non-prod domain which is not a localhost domain.

We use client only app, so my question is if someone could add some of our domains to 'allow CORS' list on your backend?