How to get Apple Pay accepted in your Gift Up! checkout
In order to accept payment using Apple Pay on your custom-built website, you will need to add your website domain to your Stripe account for "Apple Pay on the Web" transactions in your Stripe dashboard here: https://dashboard.stripe.com/settings/payment_method_domains?enabled=true.
It's also a good idea to add giftup.app, and cdn.giftup.app to the domains list, so your Gift Up hosted checkout works with Apple Pay in your Stripe account.

To test Apple Pay is working and enabled, you will need the correct hardware. Here's a guide from Apple.
If you're having any issues getting it to work, contact Stripe for advice. They do have a complete guide here: https://stripe.com/docs/stripe-js/elements/payment-request-button#verifying-your-domain-with-apple-pay