$_POST variable empty after AJAX Request

HTML

<div id="banner-message">
  <p>Send Post</p>
  <button>Send Post Ajax</button>
</div>
<img src="https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcQ-bKE_oPXorefsLMe-cFJOKSSOnGLxQ-icQ8ai4umrVMOp1ddB&usqp=CAU">
<img src="https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcSHZpkCWtUX17YT92S9kknlCmHllPYUf7qU7p8_DwVY0rLQ-Nji&usqp=CAU">
<img src="https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcQAQRXPpIVlUF6CluMs7IQ1ABAdk365roI8_XISN-c1VHGHu42b&usqp=CAU">
<img class="highlight" src="https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcS1lQqXp_ll8lmCvygRuNrfK0ctOD1TGqUDskcNNHknDL4mrwEx&usqp=CAU">
<img class="highlight" src="https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcQY7uK3oFaEMh45nDElZXrsiyxqjd6lfEwja0nFJvnfSD6lRZyC&usqp=CAU">

JavaScript

// find elements
var button = $("button")

// handle click and add class
button.on("click", function(){
  var images = document.getElementsByTagName('img');
  var images2remove = [];
  
  $(images).each(function() {
        if($(this).hasClass('highlight')) {
            var path = $(this).attr('src');
            images2remove.push(path);
        }

  });
  
  images2remove = JSON.stringify(images2remove);
  $.ajax({
        url: '/echo/json/',
        type: 'post',
        data: {'json' : images2remove},  
        
        success: function(response) {
            if(response != 0) {
              console.log(response);
            }
            else {
                alert('file not removed');
            }
        }
  });
  //console.log({'images' : images2remove});
});