您错过了使用WC会话变量来设置一些数据并在折扣函数中使用它...下面的第一个函数处理您的设置，它会加载到其他函数的任何地方。

// Settings
function get_membership_settings(){
    $discount_percentage = 1; // the discount percentage: 1% here

    return array(
        'percentage'       => $discount_percentage,
        'field_key'        => 'membership_number', // Field "name" key (or id)
        'field_type'       => 'text',
        'field_label'      =>  __('Membership number', 'woocommerce'),
        'button_text'      =>  __('Apply membership number', 'woocommerce'),
        'discount_text'    =>  sprintf( __('Membership discount%s', 'woocommerce'), ' ('.$discount_percentage.' %)' ), // for negative fee
        'valid_message'    => __('Number is valid (text message).', 'woocommerce'),
        'unvalid_message'  => __('Number not valid (text message).', 'woocommerce'),
        'empty_field_text' => __('Please enter your membership number.', 'woocommerce'),
     );
}

// Settings + Membership number
function get_membership_data(){
    $settings      = get_membership_settings();// Load settings
    $field_key     = $settings['field_key']; // The field Id

    $user_value    = get_user_meta( get_current_user_id(), $field_key, true ); // Get "membership number" from user data
    $session_value = WC()->session->get($field_key); // Get "membership number" from session variable

    // Set "membership number" in the array
    $settings['field_value'] = empty($session_value) ? $user_value : $session_value;

    return $settings;
}

购物车上显示的字段（见最后的截图）：

// Display a text input field on cart (+ javascript)
add_action('woocommerce_cart_contents', 'display_field_membership_number', 100 );
function display_field_membership_number(){
    extract(get_membership_data()); // Load data and settings

    echo '<tr><td colspan="6" class="membership" style="padding:0;border-top:16px solid #FFF;">
        <style>.message.off,label.hidden{display:none}.membership .message{margin-left:20px}</style>
        <div id="'.$field_key.'-wrapper">
            <label for="'.$field_key.'" class="hidden"> '.$field_label.'&nbsp;<abbr class="required" title="required">*</abbr></label>
            <input type="'.$field_type.'" class="input-'.$field_type.'" name="'.$field_key.'" id="'.$field_key.'" placeholder="'.$field_label.'" value="'.$field_value.'">
            <button type="button" class="button">'.$button_text.'</button>
            <span class="message off"></span>
        </div>
    </td></tr>
    <tr><td colspan="6" style="padding:0"></td></tr>';
}

jQuery/Ajax代码：

// Function that send the Ajax request | jQuery + Ajax
add_action('wp_footer', 'membership_number_js_script');
function membership_number_js_script() {
    if( ! is_cart() ) return; // Only on cart

    $field_key = get_membership_settings()['field_key']; // Load field key id

    // jQuery Ajax code
    ?>
    <script type="text/javascript">
    jQuery( function($){
        if (typeof woocommerce_params === 'undefined')
            return false;

        var s = '#<?php echo $field_key; ?>-wrapper';

        $(s+' button').click( function(){
            var value = $(s+' input').val();

            // Function that handle the display of the message
            function handleDisplayMessage( selector, response, error = false ) {
                if ( ! error ) {
                    $.each( $.parseJSON(response), function(index, value){
                        displayMessage( selector, value, index );
                    });
                } else {
                    displayMessage( selector, response, 0 );
                }
            }

            // Function that display a message
            function displayMessage( selector, response, type ) {
                $(selector).hide('0').removeClass('off').html(response).css('color', (type == 1 ? '#03C03C' : '#DC143C')).show();
                setTimeout(function() {
                    $(selector).hide();
                }, 3000 );
            }

            $.ajax({
                type: 'POST',
                url: wc_cart_params.ajax_url,
                data: {
                    'action': '<?php echo $field_key; ?>',
                    '<?php echo $field_key; ?>': value,
                },
                success: function (response) {
                    handleDisplayMessage( (s+' .message'), response );
                    $(document.body).trigger("added_to_cart"); // refresh cart
                },
                error:function(error){
                    handleDisplayMessage( (s+' .message'), ('A problem occured (error: '+error+')'), true );
                }
            });
        });
    });
    </script>
    <?php
}

PHP WordPress Ajax接收器函数：

// Get the ajax request and set value to WC session (and the field validation)
add_action( 'wp_ajax_membership_number', 'set_membership_number_and_validation' );
add_action( 'wp_ajax_nopriv_membership_number', 'set_membership_number_and_validation' );
function set_membership_number_and_validation() {
    extract(get_membership_settings()); // Load and extract settings

    if( isset($_POST[$field_key]) && ! empty($_POST[$field_key]) ) {

        ## HERE BELOW, SET YOUR CODE (that checks membership number for validation)

        $validation = true; // "true" when validated (or false if not)

        // Set membership number to a WC session variable
        WC()->session->set($field_key, $_POST[$field_key]);

        // Send response back
        echo json_encode( ($validation ? [1 => $valid_message] : [0 => $unvalid_message]) );
    } else {
        // Send response back
        echo json_encode( [0 => $empty_field_text] );
    }
    die();
}

折扣有多种方式（这里有两种，使用不同的挂钩）：

// 1. Percentage discount for Membership (with a negative fee)
add_action( 'woocommerce_cart_calculate_fees', 'add_membership_discount' );
function add_membership_discount( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    extract(get_membership_data()); // Load and extract settings + membership numver

    if( ! empty($field_value) ) {
        // Calculation
        $discount = ( $cart->get_cart_contents_total() + $cart->get_shipping_total() ) * $percentage / 100;

        $cart->add_fee( $discount_text, -$discount ); // Add a discount
    }
}

// 2. Percentage discount for Membership (on cart items price)
add_action( 'woocommerce_before_calculate_totals', 'add_membership_cart_item_discount' );
function add_membership_cart_item_discount( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    if ( did_action( 'woocommerce_before_calculate_totals' ) >= 2 )
        return;

    extract(get_membership_data()); // Load and extract settings + membership numver

    if( ! empty($field_value) ) {

        // Loop through cart items
        foreach( $cart->get_cart() as $cart_item ){
            // Get the real WC_Product Object
            $product = wc_get_product($cart_item['data']->get_id());

            $price = $product->get_price(); // The real product price

            $discounted_price = $price * ( 1 - ( $percentage / 100 ) ); // Calculation

            $cart_item['data']->set_price($discounted_price); // Set the discounted price
        }
    }
}

所有代码functions.php活动子主题（或活动主题）的文件中。测试和工作。

类似的线程：

• 客人客户查看WooCommerce订单账单电子邮件的第一个订单折扣
• WooCommerce结账页面中使用AJAX和Fee API的动态折扣