I am new to AJAX and It seems like I might be missing a quite fundamental detail.
I would like to implement a visit counter via IP address in AJAX. In PHP it takes IP addresses and stores them inside a “visitors.db” file. If I do this locally without using WordPress, it works correctly. I am sending you the link:

Demo Local

But if I create a function with WordPress it comes out:

Uncaught SyntaxError: Unexpected token < in JSON at position 0 at
JSON.parse

This is my code:

add_action( 'wp_head', 'conta_visite');
function conta_visite(){
    
    $dir = get_stylesheet_directory() . "/users";
    if (!file_exists($dir)) {
    wp_mkdir_p( $dir );
        
}
if(isset($_POST['getCustomerCount']))
{

    $dbfile = get_stylesheet_directory() . "/visitors.db"; // path to data file
    $expire = 3; // average time in seconds to consider someone online before removing from the list
    if(!file_exists($dbfile)) {
        echo json_encode(['success'=> false,'error_message'=>"Error: Data file " . $dbfile . " NOT FOUND!"]);
        die();
        //die("Error: Data file " . $dbfile . " NOT FOUND!");
    }

    if(!is_writable($dbfile)) {
        echo json_encode(['success'=> false,'error_message'=>"Error: Data file " . $dbfile . " is NOT writable! Please CHMOD it to 666!"]);
        die();
        //die("Error: Data file " . $dbfile . " is NOT writable! Please CHMOD it to 666!");
    }

    $count = CountVisitors($dbfile, $expire);
    if(is_numeric($count)){
        $out = $count; // format the result to display 3 digits with leading 0's
        echo json_encode(['success'=>'true', 'customer_count'=>$out]);
    }
    else 
    {
        echo json_encode(['success'=> false, 'error_message'=>"count is not numeric"]);
    }
}
else{
    echo $dbfile;
    echo json_encode($_POST);
}


function CountVisitors() {
    global $dbfile, $expire;
    $cur_ip = getIP();
    $cur_time = time();
    $dbary_new = array();

  $dbary = json_decode(file_get_contents($dbfile),true);
    if(is_array($dbary)) {
      
      foreach($dbary as $user_ip => $user_time){
        if(($user_ip != $cur_ip) && (($user_time + $expire) > $cur_time)) {
                $dbary_new[$user_ip] = $user_time;
            }
      }
    }
  
    $dbary_new[$cur_ip] = $cur_time; // add record for current user

    $fp = fopen($dbfile, "w");
    fputs($fp, json_encode($dbary_new));
    fclose($fp);

    return count($dbary_new);
}

function getIP() {
    if(isset($_SERVER['HTTP_X_FORWARDED_FOR']))
    {
        $ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
    }
    elseif(isset($_SERVER['REMOTE_ADDR'])) {
        $ip = $_SERVER['REMOTE_ADDR'];
    }
    else
    {
        $ip = "0.0.0.0";
    }
    return $ip;
}

    
?>

<p id="customer_count">Customers Online: <span></span></p>

    <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
    <script>
        function updateCustomerCount() {
  $.ajax({
    type: "POST",
    cache: false,
    data: {getCustomerCount: true},

        success: function(response) {

            var data = JSON.parse(response);
            //var data = response;
            console.log(response);
            if (data.success) {
                $("#customer_count span").text(data.customer_count);
            } else {
                console.log(data.error_message);
            }

        },
        error: function(response, request, status, error) {
            console.log(error);
        }
    });
setTimeout(updateCustomerCount, 2000);
} 
updateCustomerCount();
        
</script>

<?php
}

This is the Demo link in WordPress: Demo Link WordPress
You can find the counter in the upper right corner of the header.

Can you help me? Because I’m going crazy and I can’t figure out where I’m going wrong….