Why the PHP can’t see a value which is coming from ajax js?

When I get my result from the JS side the value comes true. But I want to fill the value to my PHP file, so I’ve used ajax. When I delete if isset function in PHP , I got an “undefined index” error.

HTML Side

     <form method="post" onsubmit="return false;"  class="form-inline">
     <input type="email" name="email" id="subscriber_email" placeholder="Your E-mail" >
     <button type="submit" id="subscribe_newsletter" class="btn newsbox-btn w- 
      100"onclick="gonder()">Subscribe</button>
                            
       </form>
       <div id="subscribe_message"></div>
        <p id="succes" class="mt-30"></p>

---

jS side

<script  type="text/javascript">
function gonder(){
var ad=$("input[name='email']").val();

$.ajax({
    type:"POST",
    url:"myphpfile.php",
    data:ad,   // I also tried  {'sendingData':ad} but it doesn't work.
    success:function(sonuc){
        $("#subscribe_message").html(sonuc);
        $("#succes").html(sonuc);   
        
    }
})

 }
</script>

---

And PHP side

<?php


    if(isset($_POST["ad"])){
    $x=$_POST["ad"];
    echo $x;

     }
   else{
      echo "There is nothing coming from the script.";

      }

     ?>

Answer

You’re sending a value, but you’re not sending a key with that value. So for example if the value is 123 then you’re only sending 123, nothing else. So this won’t find it because there’s no key called ad in the data being sent:

$_POST["ad"]

Add a key for the value:

data: { ad: ad }

Or even simply:

data: { ad }