Post comes empty?

Question

JavaScript

let nickname = document.getElementById("nickname");
let status = document.getElementById("status");


nickname.addEventListener("input", () => updateInfo(nickname));


function getCookie(name) {
    var cookieValue = null;
    if (document.cookie && document.cookie !== '') {
        var cookies = document.cookie.split(';');
        for (var i = 0; i < cookies.length; i++) {
            var cookie = cookies[i].trim();
            // Does this cookie string begin with the name we want?
            if (cookie.substring(0, name.length + 1) === (name + '=')) {
                cookieValue = decodeURIComponent(cookie.substring(name.length + 1));
                break;
            }
        }
    }
    return cookieValue;
}


function updateInfo(nickname){
  nicknameRequest = new XMLHttpRequest();
  
  nicknameRequest.open("POST", "/articles/checknickname/");
  
  nicknameRequest.setRequestHeader("X-CSRFToken", getCookie('csrftoken'));
  
  let params = {
    "nickname": nickname
  }
  
  nicknameRequest.send(JSON.stringify(params));
  
  nicknameRequest.onprogress = function(event){
     status.innerHTML = "...";
  }
  
  nicknameRequest.onload = function(){
    if (nicknameRequest.status == 200){
      status.innerHTML = nicknameRequest.response;
    }
  }
}

I printed out the values ​​of the post request in the console (when I receive a request to the server) and they were not there at all.