This is my absolute first try on the subject: I'm sending data throw email using javascript and PHP. I have read previous responses on the subject, but I can't make it work. My js code:

const messagesend = document.getElementById('message_form');
 messagesend.addEventListener('submit', (eee) => {
     eee.preventDefault();
     var messageData = new Object();
     messageData.name = document.getElementById('conname').value;
     messageData.email = document.getElementById('conemail').value;
     messageData.message = document.getElementById('conmessage').value;
     messageData.verification = 'drovarcrete_message';
     var messageString = JSON.stringify(messageData);
 
     $.ajax({
         type: "POST",
         contentType: 'application/json',
         url: 'messageSender.php',
         data: messageString,
         dataType: 'json',
         success: function(data) {
              alert("Message send.");
              $('#contactModal').modal('hide');
              $('#email_success_info').modal('show');
            
         }
     });

 });

 $("#modal2_close").click(function() {
     $('#email_success_info').modal('hide');
 });

My PHP works fine, with last line being: echo 'Message send'; I have also tried: echo json_encode(array('success' => true));

However, the alert message doesn't show.