Payment Request buttons visible for zero-amount checkout if coupon is appled on the checkout page

[dmvrtx]

Describe the bug

Express checkout buttons are shown for $0 checkouts. However, such amount is not supported by Stripe express checkout, leading to a lot of abandoned checkouts due to the Apple/Google pay button throwing errors when the checkout is $0.

This was fixed for block-based themes, but not for the shortcode ones, like StoreFront.

Related GH Issues:

• WooPay button appears on zero total orders #7895
• Google Pay and Apple Pay showing up on zero balance owed carts #5406

To Reproduce

• Create a simple product with a value of 20.
• Create a coupon that will discount 20 and will enable free shipping.
• Inside a Google Payments compatible browser, add the product to cart, and move to checkout.
• The express checkout button will be rendered and functional.
• Apply the discount, and that will make the checkout total 0.

Note

It is important that coupon is applied on the checkout page, when express payout buttons are already visible!

Actual behavior

Payment Request buttons, i.e. ApplePay, GooglePay and others, are visible.

Screenshots

Expected behavior

Payment Request buttons shouldn't be available.

[dmvrtx]

Update: After some testing (see notes below), I can reproduce this issue, with the caveat, that coupon code should be applied on the checkout page, once express checkout buttons are rendered.

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I've been testing the steps locally and cannot reproduce the issue. I've tried three different options, both with develop and 8.4.0 branches:

• Completely free product and shipping.
• Non-free product with coupon for 100% discount and free shipping.
• Non-free product with coupon for the exact amount and free shipping.

In all three cases express checkout buttons didn't appear on the cart and checkout pages, both block and shortcode versions.

Moreover, I didn't see any payment options suggested, and my suspicion is that WooCommerce handled the zero amount on its side, removing the need for the payment plugins to intervene.

If I remove the coupon, buttons appear as expected.

[dmvrtx]

The culprit is that for the checkout page WooPayments decides in class-wc-payments-payment-request-button-handler.php if it should show express checkout buttons or not, but this check happens once when page is loaded and is not re-evaluated when cart totals are updated. This seems to have other implications, e.g. payment request buttons won't appear if cart total goes from zero to any other value.