Web Messaging SDK file upload 400 Bad Request on PNG

NICE CXone API & Integrations
1

Stuck on the file upload flow for Web Messaging. Trying to send a simple PNG screenshot from the guest SDK but getting a 400 back immediately. The docs say PNG is fine and the file is only 200kb, well under the usual limits.

Using the standard sendFile method on the session object. Here’s the payload structure I’m passing:

session.sendFile({
 fileName: 'screenshot.png',
 mimeType: 'image/png',
 fileData: base64String // verified this is valid
});

The response body just says Invalid file type which is confusing since PNG is listed as supported.

  • Genesys Cloud Web Messaging SDK v2.1.4
  • Frontend: React 18
  • File: 200kb PNG
  • Error: 400 Bad Request

Is there a hidden MIME whitelist I’m missing or does the base64 encoding need a specific header prefix? Nothing in the console logs.