Ruby on Rails

So guys i'm working on a tournament bracket based on the GOjs library, The bracket has score input. Once my user is done editing the bracket i save the bracket into a json variable :

function save() {      var tojs = myDiagram.model.toJSON();      var payload = JSON.parse(tojs);      stringify_tojs = JSON.stringify(payload);      myDiagram.isModified = false;

I use XMLHttpRequest to able to post the payload into my rails model that handles 'payload' :

var request = new XMLHttpRequest();      request.onload = callback;      request.open("post", "http://localhost:3000/malesingles");      request.setRequestHeader("Content-Type", "application/json");      request.send(payload);

I dont know where i went wrong but i'm certain it's around my controller params but i can't find my mistake already been a week, the controller looks something like this :

@tournoi = Tournoi.new(bracket_params)    if @tournoi.save      redirect_to root_url      flash[:success] = "Your tournament bracket has been validated!"    #  redirect_to @tournoi    else      render 'new'    end

end i have included the bracket_params in private settings

def bracket_params        params.require(:tournoi).permit(:payload)       end

Tried different method to post the payload none really work, would appreciate some help to understand where i went wrong, i get a param is missing or empty :/.