Genesys Web Messaging SDK file upload MIME rejection despite valid config

We’ve got a custom web messaging widget built with the Genesys Web Messaging SDK. Everything works fine for text, but file uploads are failing. The customer tries to send a PDF, and the UI shows a generic ‘attachment failed’ error.

Looking at the browser console, I see a 415 Unsupported Media Type coming back from /api/v2/interactions/webmessaging/messages. Here’s the payload we’re sending:

{
 "interactions": [{
 "type": "webmessaging",
 "to": {"id": "some-conversation-id"},
 "content": {
 "type": "file",
 "fileName": "contract.pdf",
 "fileSize": 245000,
 "mimeType": "application/pdf"
 }
 }]
}

The file is well under the default 10MB limit. I’ve checked the webMessagingSettings in our org via the API, and allowedFileTypes includes application/pdf. The Terraform state for the engagement channel shows the setting is correctly applied.

Is there a caching issue with the SDK configuration? Or does the Web Messaging API have a stricter allowlist than the org settings imply? I’m using SDK version 2.4.1.