I'm trying to perform an action with AJAX in a Child theme template in Wordpress. I've looked into many similar issues. However, I couldn't find a solution. I've been dealing with this for about 2 hours. I'll be glad if anyone can help.

I have checked the error.log file several times. However, there is no problem.I am getting the following error in the browser console:

XHRPOSThttps://example.com/wp-admin/admin-ajax.php [HTTP/3 400 Bad Request 905ms]


<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
    <button type="button" id="continue_process" onclick="continue_process()">Continue</button>
        function continue_process() {
            var ajax_nonce  = '<?php echo wp_create_nonce( "before_process_nonce" ); ?>';
            var ajax_url    = '<?php echo admin_url( "admin-ajax.php" ); ?>';
                url         : ajax_url, /* WordPress AJAX endpoint.*/
                method      : 'post',
                data : {
                    'action'        :'x_before_process',
                    'security'      :ajax_nonce
            success : function( response ) {
                /* Get AJAX data from */
                const obj = JSON.parse(response);
            error : function( err ) {
                /*Error */


if ( ! defined( 'ABSPATH' ) ){exit; /*Exit if accessed directly*/ }
add_action("wp_ajax_nopriv_x_before_process", "x_before_process");

function x_before_process() {
    if(!wp_verify_nonce( sanitize_key($_POST['security']), 'before_process_nonce' )){
        wp_send_json_error('Invalid nonce');

    $message = ['type'=>'success','message'=>'True'];

1 Answer 1


It has nothing to do with child themes, the problem is here:

add_action("wp_ajax_nopriv_x_before_process", "x_before_process");

Notice the nopriv, this is for logged out users, but it's likely you are logged in

This needs adding:

add_action("wp_ajax_x_before_process", "x_before_process");

Note that this would not have been an issue if it was built using a more modern AJAX API such as the WP REST API

  • There is no problem there. What I want is for users who are not already logged in. I found the problem. But I don't know why. If I move php code to function.php (in child theme) I don't get 400 Bad error. Why could this be? So, in process-ajax.php this will not work. Commented Mar 28, 2023 at 15:37
  • a HTTP 400 and a response of 0 indicates no handler was found, how and where are you loading process/process-ajax.php? Note that the nopriv handler only works for logged out users, it does not work for logged in users. Also have you confirmed the nonce check is not the problem?
    – Tom J Nowell
    Commented Mar 28, 2023 at 15:48
  • Maybe not working because of Wordpress caching system. As it said at the beginning, the HTML/JS content is here: themes/child-theme/process/template.php . Also here is the PHP content, the part where I can meet the ajax request: themes/child-theme/process/process-ajax.php . If I move this part, PHP part, here (themes/child-theme/function.php) the problem is solved. Strange. Commented Mar 28, 2023 at 15:53
  • how is process-ajax.php being loaded though? Is it a require in the function.php file? Is the file being included in code that runs on a hook? From inside an object/function? Is it being included from a template file?
    – Tom J Nowell
    Commented Mar 28, 2023 at 16:05
  • Yes, that's what I missed unfortunately. I thought of this now. Thank you. Do you think it makes sense to use the after_setup_theme hook? Commented Mar 28, 2023 at 16:12

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