Empty CALLBACK_OBJECTS content when using HTTP callback persistance

I am using the y-websocket provider and I am trying to implement persistence through the HTTP Callback method.
I am running the server by setting npm start command to: set HOST=localhost&&set PORT=1234&&set CALLBACK_URL=http://localhost:5000/savecontent&&set CALLBACK_OBJECTS={\"prosemirror\":\"XmlFragment\"}&& npx y-websocket-server

Unfortunately when my callback api is hit I receive empty “content” property. The contents of the editor are not supplied.
As a text editor I use SlateJs and for the binding between YJS and SlateJs I am using https://github.com/BitPhinix/slate-yjs

What is the correct CALLBACK_OBJECTS configuration in order to receive the editor content which I can persist through my API?

Thanks!

Hi @Bogatinovski,

How do you connect to the y-websocket server? Could you share the client-code related to Yjs?