Web Messaging File Upload: MIME validation and 413 errors on binary payloads

Could someone explain the exact constraints for file uploads in the Web Messaging guest API? We are building a Django backend to process inbound messages from Genesys Cloud. Our Celery workers are receiving payloads via webhook, but we hit intermittent 413 errors when customers upload PDFs larger than 5MB. The documentation mentions a limit, but it is vague on whether this applies to the initial upload request or the subsequent media resource fetch.

We are using the guest API to simulate uploads for testing:

import requests

headers = {
 'Authorization': f'Bearer {token}',
 'Content-Type': 'multipart/form-data'
}
files = {'file': open('test.pdf', 'rb')}
response = requests.post(
 'https://api.mypurecloud.com/api/v2/conversations/messaging/media',
 headers=headers,
 files=files
)

The 413 error suggests the payload is too large, but I suspect it might be a MIME type issue. Does the API reject non-standard binary types before size validation? We need to validate these on the Django side before sending to Celery to avoid worker crashes.

Thanks for the help.

If you check the docs, they mention the 5MB limit applies to the initial POST request body, not the media resource fetch. You are likely hitting the server-side limit on the webhook receiver, not Genesys. Adjust your Nginx or Apache config to allow larger payloads. Set client_max_body_size 10M; in your server block. Verify the content-type is multipart/form-data. If you are using SvelteKit server routes, ensure the hook handles the binary stream correctly. Do not try to base64 encode the file in the frontend; it increases payload size by 33%. Use the media ID returned in the webhook payload to fetch the file directly from the Genesys CDN. This bypasses your server’s upload limit entirely. Check the contentLength header in the webhook payload to log incoming sizes. If the error persists, enable debug logging on your backend to see where the request drops. This pattern works for our internal status widget.