Yii2 Pass variable from Ajax to controller?

Question

Yii

Hello.
Can you please tell me how to pass the value of the variable to the controller from this ajax script?

$(document).ready(function(){
   $("#events-select").change(function(){
     var month = $("#events-select :selected").val();
       $.ajax({
          type: "POST",
           url: "web/site/events",
           data: {"month": month},
           cache: false,
           success: function(response){
               $(".events").html(response);
           }
       });
   });
});

Through alert, the variable is displayed, but when I try to do this in the controller:

public function actionEvents()
{
    if (isset($_POST)){
            $meet = $_POST['month'];
        }
    return $this->render('events');
}

I get the error Undefined index: month
How to implement this correctly?
Thanks in advance.