I have working requests code in python and need it in ajax

var jsonData = {"x":"y"};

$.ajax({
  url: url,
  type: 'POST',
  data: jsonData,
  //dataType: "JSON",
  
  error: function(e) {
    console.log(e);
  }
  
});

json: jsonData, JSON.stringify, 'Content-Type': 'application/json' and changing names doesn't work, I tried a lot of things, but everytime error 400

this python code works fine

payload = {
    'a':'b',
    'a': 'b'
}


#but it doesn't work with field 'data' or 'params', must be named 'json'
r = requests.post(url, json=payload) #data=payload won't work, otherwise error 400
print(r.text)