[WooCommerce Checkout] Coupon "Apply" button triggers full order submission (?wc-ajax=checkout) instead of applying discount

[POBrien333]

Description

When using the Breakdance WooCommerce Checkout element, clicking the "Apply coupon" button (or pressing the Enter key inside the coupon input field) submits the entire checkout form (?wc-ajax=checkout) rather than firing the isolated coupon AJAX handler (?wc-ajax=apply_coupon).

As a result, WooCommerce runs full validation on all required checkout fields (e.g., Billing First/Last Name, T&Cs acceptance) and returns validation errors instead of applying the discount code to the cart totals.

Steps to Reproduce

1. Create a checkout page using the Breakdance WooCommerce Checkout element.
2. Add any item to the cart and proceed to /checkout/.
3. Leave all billing/shipping input fields blank.
4. Enter a valid coupon code in the coupon field.
5. Click Apply coupon (or press Enter while typing in the input box).

Expected Behavior
An AJAX request to ?wc-ajax=apply_coupon or ?wc-ajax=update_order_review should fire.
The cart totals should update dynamically without triggering form validation on billing/shipping fields or terms & conditions.

Actual Behavior
The form makes a POST request to ?wc-ajax=checkout.
WooCommerce attempts to place the order and returns validation errors in the response payload:
JSON
{ "result": "failure", "messages": "<ul class=\"woocommerce-error\" role=\"alert\"><li>Billing First name is a required field.</li><li>Please read and accept the terms and conditions...</li></ul>" }

Root Cause / Technical Details
Inspecting the rendered DOM shows that the coupon button is output with type="submit" inside the main <form class="checkout woocommerce-checkout">:
HTML
<button type="submit" class="button" name="apply_coupon" value="Apply coupon">Apply coupon</button>

Because event handlers on the button do not intercept and run preventDefault(), the browser treats it as a standard form submit button, dispatching the entire checkout payload.

I was able to fix it with some JavaScript, but suggest this should be fixed globally. Thanks.

You should also include the following information:

• Breakdance version: 2.8.1
• Browser & OS: Win11 and Firefox 153.0.3 (64-bit)
• If you receive any kind of error message, you should also provide your PHP (8.3) and WordPress version (7.0.3)