درود
ساختارها مشابه آموزش است اما نمی‌توانم محصول را اضافه کنم. بنظر شما دلیلش چه چیزی می‌تواند باشد؟
فایل dashboard-ajax.js:

jQuery(document).ready(function ($) {
    $('#add_product').on('submit', function (e) {
        e.preventDefault();
        // alert('ajax');
        let name = $('#name').val();
        let brand = $('#brand').val();
        let model = $('#model').val();
        let price = $('#price').val();
        let status = $('#status').val();
        let nonce = $('#test-1').val();
        $.ajax({
            url: '/wp-admin/admin-ajax.php',
            type: 'post',
            data: {
                action: 'add_product',
                name: name,
                brand: brand,
                model: model,
                price: price,
                status: status,
                nonce : nonce
            },
            success: function (response) {
                console.log(response);
            },
            error: function (error) {
            }
        });
    });
    $('.delete-product').on('click',function (){
        let el = $(this);
        let product_ID = el.data('id');
        let nonce = el.data('nonce');
        // alert(product_ID);
        $.ajax({
            url: '/wp-admin/admin-ajax.php',
            type: 'post',
            data: {
                action: 'delete_product',
                product_ID: product_ID,
                nonce:nonce
            },
            beforeSend : function (){
                el.removeClass('fa-times-circle').addClass('fa-sync fa-spin');
            },
            success: function (response) {
                if(response.success){
                    // alert(response.message);
                    // Swal.fire(response.message);
                    Swal.fire({
                        position: 'center',
                        icon: 'success',
                        title: response.message,
                        showConfirmButton: false,
                        timer: 1500
                    })
                    el.parents('tr').remove();
                }
            },
            error: function (error) {
            },
            complete : function (){
            }
        });
    })
    $('.select-product').on('click',function (){
        let el = $(this);
        let product_ID = el.data('id');
        $.ajax({
            url: '/wp-admin/admin-ajax.php',
            type: 'post',
            data: {
                action: 'find_product_by_ID',
                product_ID: product_ID
            },
            success: function (response) {
                let data = JSON.parse(response);
                // console.log(data);
                $('#p_ID').val(data.ID);
                $('#p_name').val(data.p_name);
                $('#p_brand').val(data.p_brand);
                $('#p_model').val(data.p_model);
                $('#p_price').val(data.p_price);
                $('#p_status').val(data.p_status);
            },
            error: function (error) {
            }
        });
    })
    $('#update_product').on('submit', function (e) {
        e.preventDefault();
        // alert('ajax');
        let p_ID = $('#p_ID').val();
        let p_name = $('#p_name').val();
        let p_brand = $('#p_brand').val();
        let p_model = $('#p_model').val();
        let p_price = $('#p_price').val();
        let p_status = $('#p_status').val();
        $.ajax({
            url: '/wp-admin/admin-ajax.php',
            type: 'post',
            dataType: 'json',
            data: {
                action: 'update_product',
                p_ID :p_ID,
                p_name: p_name,
                p_brand: p_brand,
                p_model: p_model,
                p_price: p_price,
                p_status: p_status
            },
            success: function (response) {
                console.log(response);
                if(response.success){
                    // alert(response.message);
                    // Swal.fire(response.message);
                    Swal.fire({
                        position: 'center',
                        icon: 'success',
                        title: response.message,
                        showConfirmButton: false,
                        timer: 1500
                    })
                }
            },
            error: function (error) {
                if(error.error){
                    // alert(error.responseJSON.message);
                    Swal.fire({
                        position: 'center',
                        icon: 'error',
                        title: error.responseJSON.message,
                        showConfirmButton: false,
                        timer: 1500
                    })
                }
            }
        });
    });
});

فایل products.php:

<?php
add_action('wp_ajax_add_product', 'add_product');
function all_product()
{
	global $wpdb;
	$table = $wpdb->prefix . 'products';
	$stmt = $wpdb->get_results("SELECT * FROM $table");
	if ($stmt) {
		return $stmt;
	}
	return false;
}
function add_product($name, $brand, $model, $price, $status)
{
	global $wpdb;
	$table = $wpdb->prefix . 'products';
	// Check for empty values or any other validation
	$data = array(
		'name'   => $name,
		'brand'  => $brand,
		'model'  => $model,
		'price'  => $price,
		'status' => $status,
	);
	$wpdb->insert($table, $data);
	if ($wpdb->insert_id) {
		return true;
	} else {
		return false;
	}
}

تصویر از وضعیت خطا: