Kettering XML and PDFs

Hi All

I’m new and would like some help please. I’m currently developing a service to send messages on MESH using the below spec.

The service work well with plain text in the body. But now I need to send PDFs, I have seen that the best way may be using Kettering XML. I have tried just simply sending a example as a body through the MESH API, but it fails (Bad Request). What am I doing wrong?

Once I have got my simple Kettering xml sending, I would like to alter it, so I contains a pdf body. Guessing this is sending a base 64 string of the pdf in the below section?

Any help would be a help, thanks

            <Cuid IdScope="Message">2</Cuid>