I've been trying to use the notifications protocol based on WebSockets as stated in the documentation, but without success.
I've managed to get it working until the subscription creation with the POST request to the websocket url:

    const createSubResponse = await fetch("https://localhost/.notifications/WebSocketChannel2023/", {
        method: "POST",
        headers: {
            "Content-Type": "application/ld+json",
        },
        body: JSON.stringify({
            "@context": ["https://www.w3.org/ns/solid/notification/v1"],
            "type": "http://www.w3.org/ns/solid/notifications#WebSocketChannel2023",
            "topic": resourceUrl,
        }),
    })

The server respons with 422 Unprocessable Entity, responding Unable to process notification channel: Missing expected value <http://www.w3.org/ns/solid/notifications#WebSocketChannel2023> - http://www.w3.org/1999/02/22-rdf-syntax-ns#type

The object I am using is 1:1 to the one provided in the documentation, I just set the correct content type of the body before sending the request.