Can I use Apple Pay within apps or on the web with Safari?
Yes, you can use Apple Pay for in-app payments or on the web with Safari at participating merchants.
Simply select the “Buy with Apple Pay” button at checkout. Review the payment information and contact details. If you need to, you can change your billing, shipping and contact information.
You will then be asked to authenticate with Touch ID or a device passcode on iPhone or iPad. On your Apple Watch, double-click the side button. The ‘Done’ icon will appear on the screen.
For more information see the Apple Pay support page.