Guest API - File Uploads Failing Intermittently - 400 Bad Request - 'fileSize'

General Discussion
1

Hey everyone! :waving_hand:

I’m hoping someone can point me in the right direction here. We’re building a custom chat widget using the WebSocket Guest API - specifically, we’re trying to get file uploads working reliably! We’ve got around 800 agents, and this is becoming a real pain point.

Everything seems set up correctly, but we’re seeing intermittent failures when users attempt to upload files larger than about 2MB. The API is responding with a 400 Bad Request, and the error message in the console is pretty unhelpful: "{\"error\":\"Invalid request\",\"message\":\"fileSize\"}". It’s just… fileSize? :face_with_raised_eyebrow:

We’re using the sendMessage method with the attachment parameter, and we’ve verified that the file data is being correctly serialized and sent as a base64 encoded string. We’re on Genesys Cloud v38.0.0 and using the latest Guest API SDK (v3.1.2). The Architect flow has a simple “Send Web Chat Message” node, nothing custom there.

The interesting thing is, smaller files (under 2MB) upload perfectly every time! It feels like there’s a size limit being enforced somewhere, but we can’t find any documentation specifying a hard limit on file sizes for the Guest API. We’ve checked our tenant’s file upload limits in Admin - those are set to 25MB.

Here’s a snippet of the code we’re using:

const payload = {
 text: 'Here’s my file!',
 attachment: {
 filename: 'report.pdf',
 contentType: 'application/pdf',
 content: base64File
 }
};

chat.sendMessage(payload)
 .then(response => console.log('Message sent!', response))
 .catch(error => console.error('Error sending message', error));

We’ve been poking around in the network tab, and it looks like the entire payload is being sent - it isn’t getting truncated before the error. It’s just the API seemingly rejecting the request. The errors aren’t consistent either, sometimes it’s immediate, other times it takes a few seconds.

Is there a size limit that’s not documented? Or could this be a server-side issue? We’ve tried different file types (PDF, JPG, DOCX) and it doesn’t seem to be file-type specific. It’s just large files, and it’s happening randomly. It’s really frustrating! :weary_face:

Any thoughts?

2

Thanks !

Problem - seeing 400s on file uploads with the Guest API isn’t unusual. It’s almost always the file size or the content type. We’re on Genesys Cloud, and hitting those limits is easy when you’ve got a lot of users.

Here’s what’s usually happening. CXone’s Guest API has strict limits. You’ll find them in the documentation (ugh, I know) but generally it’s around 10MB max file size. Also, they’re picky about content types - only certain ones are allowed.

Here’s a quick repro/fix.

  1. Validate client-side: Before you even try to send the file, check the size in JavaScript. Something like this:
function checkFileSize(file) {
 const maxSizeInMB = 10;
 const maxSizeInBytes = maxSizeInMB * 1024 * 1024;
 if (file.size > maxSizeInBytes) {
 alert("File size too large. Max 10MB");
 return false;
 }
 return true;
}
  1. Content type check: Same deal - make sure the content type is in CXone’s approved list. You can get that list in the docs.
  2. Data Action pre-check: Wrap the API call in a Data Action. This lets you add some extra logging/error handling and, crucially, check the size/type again before it hits the CXone API.

We’ve seen cases where the front-end validation fails. Adding a Data Action check is a good safety net. It’s a bit of overhead, but avoids those intermittent 400s in prod.

Anyone seen this?