Web Messaging SDK file upload MIME type validation failing

Hey folks,

Stuck on a weird edge case with the Genesys Cloud Web Messaging SDK (v1.2.4). We’re trying to let customers upload PDF contracts and image receipts, but the sendFile method is throwing a 400 Bad Request error for seemingly valid files.

Here’s the setup. I’m initializing the guest session normally, then calling:

await guest.sendFile({
 file: fileObj,
 name: 'contract.pdf',
 mimeType: 'application/pdf'
});

The fileObj is a standard File object from an <input type="file"> element. I’ve verified the fileObj.type is application/pdf and the size is well under the 5MB limit (it’s about 200KB). Yet the API responds with:

{
 "code": 400,
 "message": "Invalid file type or size",
 "status": "Bad Request"
}

It’s not just PDFs. JPEGs are also getting rejected with the same message. PNGs work fine. This feels like a MIME type mapping issue on the server side, but the docs list application/pdf and image/jpeg as supported.

I tried manually overriding the mimeType in the payload to image/jpeg for a JPEG file, but that didn’t help. The error persists. Is there a hidden whitelist of MIME types that’s different from the public docs? Or am I missing a step in how the SDK packages the file before sending?

Also, the SDK doesn’t give any client-side validation errors before sending, which makes debugging this a pain. I have to wait for the network request to fail. Any ideas on how to pre-validate the file type before calling sendFile?

Thanks.