Missing validate-required CSS class breaks Stripe payment method creation

Custom checkout fields of type radio, select, multicheckbox, multiselect and file rendered by this plugin are missing the validate-required CSS class on their wrapper element when marked as required, even though the field is correctly flagged required => true in the PHP field definition.

The cause is in lib/view/frontend/class-fields-filter.php, method custom_field():

if ( $args['required'] ) {
    // $args['class'][] = 'validate-required';
    $required = '&nbsp;<abbr class="required" title="' . esc_attr__( 'required', 'woocommerce-checkout-manager' ) . '">*</abbr>';
}

The line that adds the validate-required class to $args['class'] is commented out. As a result, the field visually shows a required asterisk, but the rendered <p class="form-row ..."> wrapper never receives validate-required.

This class is the standard convention WooCommerce core (and other plugins) use client-side to detect empty required fields during checkout validation.

Impact:

This went unnoticed for a long time because it only affected the visual “empty required field” highlighting for these field types. However, WooCommerce Gateway Stripe 10.9.0 (released 2026-08-17) added stricter client-side validation of required billing fields before creating/confirming the Stripe payment intent (see their changelog: “Validate customer details against required billing fields from checkout before sending to Stripe”, “Prevent unnecessary Stripe payment method creation when shortcode checkout has empty required fields”).

Because of the missing validate-required class, this new Stripe logic gets confused for sites that have at least one required radio/select/multicheckbox/multiselect/file field added via this plugin. The practical symptom: checkout fails on every single order paid by Stripe (card), with the WooCommerce Stripe log showing:

The information for creating and confirming the intent is missing the following data: payment_method.

i.e. the checkout form submits to the server, but the client-side Stripe payment method (pm_xxx) was never attached before submission.

Steps to reproduce:

1. Add a required custom billing field of type “Multiple checkbox” (or radio/select/multiselect/file) via WooCommerce Checkout Manager.
2. Enable WooCommerce Gateway Stripe 10.9.0+ with the credit card (UPE) payment method.
3. Go through checkout and pay by card.
4. Payment fails; WooCommerce > Status > Logs > woocommerce-gateway-stripe shows the “missing payment_method” error above.
5. Disabling WooCommerce Checkout Manager, or removing the “required” flag from the affected field, makes checkout succeed again.

Suggested fix:

Uncomment the line in class-fields-filter.php:

if ( $args['required'] ) {
    $args['class'][] = 'validate-required';
    $required = '&nbsp;<abbr class="required" title="' . esc_attr__( 'required', 'woocommerce-checkout-manager' ) . '">*</abbr>';
}

so the rendered markup matches what the field definition already declares.