If the merchant desires to collect additional information not part of the API
(e.g., additional delivery instructions), the merchant can show a page with
<input> fields after the checkout..
For the purposes of the demo, imagine you have chosen an item and now you need to
check out. Please note that no payments will be taken, this is just a front-end
demo. If you would like to try entering card details, you can use dummy data,
for example the card number
4111 1111 1111 1111.
Payment Request success. Demo complete. No payment has been taken.
The Payment Request API is unsupported or was cancelled or failed, so here we can proceed with our legacy web form (not implemented for this demo).