Ajax doesn't work. it doesn't show any errors

I am using Ajax in my application. Previously it worked fine and checked many times. Not working now. I didn't change anything in this code.

I checked the URL path and also checked the Jquery click event.

It doesn't show any errors in the console log.

$(".submit").click(function(event) {
    event.preventDefault();
    var month = $("#month").val();
    var zone = $("#zone").val();    
    $.ajax({
      type: 'POST',
      url: '<?php echo base_url().'index.php/ContMain/generate'; ?>',
      dataType: 'json',
      data: {month: month, zone: zone},
      success: function(res) {  
         alert(res);
      }

   });
});