Web Messaging SDK: Handling file upload MIME type validation

I’m building a custom guest UI wrapper for Web Messaging. Need to handle file uploads from the client side before hitting the API. The docs are vague on specific MIME type limits. I tried sending a .psd file and got a 415 Unsupported Media Type.

Is there a list of accepted MIME types in the SDK docs or do I need to hardcode validation? Also, what’s the hard size limit for the upload endpoint?