Js variable to php using ajax

Question

I’m trying to send a string of 13 ASCII characters from js to the PHP session using Ajax, but on receiving string is not the same as I send it, using JSON.stringify and json_decode does nothing.

    console.log(plik_T[click])
    jQuery.ajax({
        type: "POST",
        url: './Setyb.php',
        dataType: 'text',
        data: {send: plik_T[click]},
        success: function (obj) {
           console.log(obj)
        }
        
    });

<?php
    var_dump($_POST['send']);
?>

I tried using JSON.stringify or changing meta UTF-8 to older versions none of this resolved my problem. Then I tried checking the type of variables which both were string, so that led me to nothing. what I'm trying to accomplish is to set my Session variable up on user click and use it in the next php page