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

Question

In wp-admin I have a table that extracts data from the database (data comes from a form filled in by users) . The request to the database to delete some elements is contained in form-plugin.php (plugins directory), function 'delete_custom_form_data()'.

the table structure and the database ID delete button is contained in functions.php

The delete.js file in /js takes the ID from functions.php and passes it to form-plugin.php, which respectively deletes the element from the database.

Whatever I do, delete.js still gives error 400 on request to form-plugin

functions.php:

function display_custom_form_data() {
    global $wpdb;
    $table_name = $wpdb->prefix . 'custom_form_data';
    $data = $wpdb->get_results("SELECT * FROM $table_name", ARRAY_A);
    ?>
    
    <div class="wrap">
        <h2>Jurnalul programărilor</h2>
         <input type="hidden" id="ajax-url" value="<?php echo admin_url('admin-ajax.php'); ?>">
        <table class="wp-list-table widefat striped">
            <thead>
                <tr>
                    <th>ID</th>
                    <th>Nume</th>
                    <th>Email</th>
                    <th>Telefon</th>
                    <th>Specializare</th>
                    <th>Data Programării</th>
                    <th>Ora Programării</th>
                    <th>Data Aplicării</th>
                    <th>Acțiune</th>
                </tr>
            </thead>
            <tbody>
                <?php foreach ($data as $row): ?>
                
                    <tr>
                        <td><?php echo $row['id']; ?></td>
                        <td><?php echo $row['name']; ?></td>
                        <td><?php echo $row['email']; ?></td>
                        <td><?php echo $row['phone']; ?></td>
                        <td><?php echo $row['spec']; ?></td>
                        <td><?php echo $row['date']; ?></td>
                        <td><?php echo $row['time']; ?></td>
                        <td><?php echo $row['sub_time']; ?></td>
                        
                      <td><button class="delete-button" data-id="<?php echo $row['id']; ?>">Șterge</button></td>
                    
                      
                    </tr>
                <?php endforeach; ?>
                 
            </tbody>
        </table>
    </div>

    <?php
}

add_action('admin_menu', 'custom_form_admin_page');

add_action('admin_menu', 'custom_form_admin_page');

delete.js:

document.addEventListener('DOMContentLoaded', function() {
    const ajaxUrlElement = document.getElementById('ajax-url');
    if (ajaxUrlElement) {
        const ajaxUrl = ajaxUrlElement.value;
        const deleteButtons = document.querySelectorAll('.delete-button');

        deleteButtons.forEach(function(button) {
            button.addEventListener('click', function() {
                const id = encodeURIComponent(this.getAttribute('data-id'));

                if (confirm('Ești sigur că vrei să ștergi acest rând?')) {
                    fetch(ajaxUrl, {
                        method: 'POST',
                        headers: {
                            'Content-type': 'application/x-www-form-urlencoded; charset=UTF-8'
                        },
                        body: 'action=delete_custom_form_data&id=' +id
                    })
                    .then(response => {
                        if (!response.ok) {
                            throw new Error('Network response was not ok. Status: ' + response.status + '. Body: ' + response.statusText);
                        }
                        location.reload();
                    })
                    .catch(error => {
                        console.error('There has been a problem with your fetch operation: ', error);
                    });
                }
            });
        });
    }
});

plugin/form-plugin.php:

function delete_custom_form_data() {
   
    if (isset($_POST['id'])) {
        
        $id = $_POST['id'];
       
        error_log('ID-ul primit pentru ștergere: ' . $id);

      
        global $wpdb;
       
        $table_name = $wpdb->prefix . 'custom_form_data';
        
        
        $result = $wpdb->delete($table_name, array('id' => $id));

        
        if ($result === false) {
           
            echo 'Eroare la ștergerea rândului cu ID-ul ' . $id;
        } else {
            
            echo 'Rândul cu ID-ul ' . $id . ' a fost șters cu succes!';
        }
    } else {
        
        echo 'ID-ul nu a fost furnizat.';
    }
}


add_action('admin_post_custom_delete_action', 'delete_custom_form_data');
add_action('admin_post_nopriv_custom_delete_action', 'delete_custom_form_data');

Am căutat mai multe soluții, dar nu am reușit să găsesc cauza problemei