I need to add a parent to each parameter in fetch method.

let endpoint = "https://www.google.it";

var urlencoded = new URLSearchParams();
urlencoded.append("test", "test");

    var requestOptions = {
        method: 'POST',
        body: urlencoded, // <--- this will send a paramenter with "test": "test"
        redirect: 'follow'
    };

I need to put parameter before "test" my expected is:

{"message": { "test": "test" }}