wp-admin/admin-ajax.php 400 (Bad Request) plugin

Question

There is a strange and frustrating behavior of the wordpress file admin-ajax.php, when I make an ajax request, it returns an incorrect 404 error request.

function rp_add_header() {
    if (is_single() || is_page()) { 
        // include the jquery Ajax/form validation javascript file
        wp_enqueue_script( 'ajax-script', plugin_dir_url(__FILE__).'rp-script.js', array('jquery'), 1.0 ); // jQuery will be included automatically

        // create the three Ajax variables used in your template file
        wp_localize_script( 'ajax-script', 'ajax_object', array(
                        'ajaxurl' => admin_url( 'admin-ajax.php' ),
                        'errorEmpty' => __( 'You need to select one of the options.' )
                )
        );

        add_action( 'wp_ajax_ajax_action', 'ajax_action_stuff' ); // ajax for logged in users
        add_action( 'wp_ajax_nopriv_ajax_action', 'ajax_action_stuff' ); // ajax for not logged in users


    }
}
add_action('wp_head','rp_add_header',1);



function ajax_action_stuff() {
    global $mail_report_to;
    $resp['status'] = 'error';
    $resp['errmessage'] = '';
    if (!empty($_POST['report-msg'])) {
        $report_msg = $_POST['report-msg'];
        $report_url = $_POST['posturl'];
        $subject = 'Post report['.get_option('blogname').']';
        $header = 'From: '.get_option('blogname').' <'.get_option('admin_email').'>' . "\r\n";
        $message = '
Someone has reported a post:
Report: '.$report_msg.'
Post URL: '.$report_url.'
Visitor IP: '.$_SERVER['REMOTE_ADDR'].'
Date/time: '.date('Y-m-d H:i:s');
        if ( wp_mail($mail_report_to, $subject, $message, $header) ) {
            $resp['status'] = 'success';
            $resp['errmessage'] = 'Your report is submitted, thanks.';
        } else {
            $resp['errmessage'] = 'Something went wrong, please try again later.';
        }
    } else {
        $resp['errmessage'] = 'Please select one of the options.';
    }
    header( "Content-Type: application/json" );
    echo json_encode($resp);
    exit;
}

I have removed all the plugins and the problem persists, any idea?

Answer 1

You're only hooking your AJAX response inside wp_head():

function rp_add_header() {
    if (is_single() || is_page()) { 
        // etc.

        add_action( 'wp_ajax_ajax_action', 'ajax_action_stuff' ); // ajax for logged in users
        add_action( 'wp_ajax_nopriv_ajax_action', 'ajax_action_stuff' ); // ajax for not logged in users


    }
}
add_action('wp_head','rp_add_header',1);

But wp_head doesn't run on admin-ajax.php, so your callbacks will never be hooked. You need to move these hooks outside of that function:

function rp_add_header() {
    // etc.
}
add_action( 'wp_head', 'rp_add_header', 1 );

function ajax_action_stuff() {
    // etc.
}
add_action( 'wp_ajax_ajax_action', 'ajax_action_stuff' ); // ajax for logged in users
add_action( 'wp_ajax_nopriv_ajax_action', 'ajax_action_stuff' ); // ajax for not logged in users