Web Messaging SDK: File upload fails with 415 Unsupported Media Type for PDFs

My current config is completely failing when attempting to enforce strict MIME type validation on customer file uploads in the Genesys Cloud Web Messaging channel.

I am currently integrating the Genesys Cloud Web Messaging SDK (v1.4.2) into a custom React frontend. The requirement is to allow customers to upload only PDF and JPEG files, with a maximum size of 5MB. I have configured the fileUpload options in the widget initialization, but the platform consistently rejects valid PDF files with a 415 Unsupported Media Type error, even though the Content-Type header in the request payload appears correct (application/pdf).

Here is the initialization code I am using:

const widget = new GenesysCloudWebMessaging({
 orgId: 'my-org-id',
 clientId: 'my-client-id',
 containerId: 'gc-web-messaging-container',
 fileUpload: {
 enabled: true,
 maxFileSize: 5242880, // 5MB
 allowedTypes: ['application/pdf', 'image/jpeg']
 }
});

When a user selects a valid PDF file, the browser console logs the following network error:

POST https://api.mypurecloud.com/api/v2/conversations/messaging/messages 415 (Unsupported Media Type)

The JSON body sent in the POST request looks like this:

{
 "attachments": [
 {
 "name": "invoice.pdf",
 "contentType": "application/pdf",
 "size": 124000,
 "data": "base64encodedstring..."
 }
 ],
 "text": "Please see attached invoice."
}

I have verified that the data field contains a valid base64 string. I also checked the Genesys Cloud API documentation for /api/v2/conversations/messaging/messages, and it states that application/pdf is supported. However, the error persists. Is there a specific server-side configuration in the Web Messaging channel settings that overrides the SDK’s allowedTypes? Or am I missing a required header in the request? I have tried adding Accept: application/json and X-Genesys-Application-Id headers, but the result is the same. Any insights on how to debug this MIME type rejection would be appreciated.

The official documentation states the fileUpload configuration in the SDK widget init only handles client-side validation and UI constraints. It does not dictate the HTTP Content-Type headers sent during the actual file transfer to the Genesys Cloud backend. You are likely hitting a mismatch where the browser sends application/octet-stream for PDFs, and the backend rejects it because strict validation is enabled on your specific channel configuration.

Check your Web Messaging channel settings in the Admin console. Ensure that application/pdf and image/jpeg are explicitly allowed in the MIME type whitelist. The 415 error is a server-side rejection, meaning the SDK successfully sent the file, but the API gateway flagged the content type. You can verify the exact header being sent by inspecting the Network tab in your browser’s developer tools during the upload process.

If the Admin settings look correct, try forcing the MIME type in your React code before passing the file object to the SDK. Create a new File object with the correct type property. This ensures the FormData payload carries the expected header. I use this pattern in my ServiceNow integrations to avoid similar issues when pushing attachments via the Platform API. It is a small fix but saves hours of debugging.

This seems like a classic SDK vs REST boundary confusion. The Web Messaging SDK handles the UI, but file uploads route through the Conversations API, where you must explicitly set Content-Type: application/pdf in your fetch or XMLHttpRequest payload before sending to /api/v2/conversations/web/{conversationId}/files.

This seems like a classic SDK vs REST boundary confusion. The Web Messaging SDK handles the UI, but file uploads route through the Conversations API. You must explicitly set Content-Type: application/pdf in your fetch or XMLHttpRequest payload before sending to /api/v2/conversations/web/{conversationId}/files.

1. Intercept the file selection event in your React component.
2. Verify the MIME type manually before initiating the upload.
3. Construct the multipart form data with the correct headers.

const uploadFile = async (file, conversationId) => {
 const formData = new FormData();
 formData.append('file', file, file.name);

 const response = await fetch(`/api/v2/conversations/web/${conversationId}/files`, {
 method: 'POST',
 headers: {
 'Authorization': `Bearer ${accessToken}`,
 // Do not set Content-Type here; let browser set boundary
 },
 body: formData
 });
 
 return response;
};

Ensure your OAuth token has conversations:write scope. The 415 error usually stems from the backend rejecting application/octet-stream when strict validation is enabled on the channel.