Login to the Magento backend and go to System > Configuration > Sales > Payment Methods. Expand the Subscribe Pro Vault | Apple Pay section.
- Turn on the "Enabled" setting and optionally the "Enabled for Non-Subscription Transactions" setting.
- On an Apple device that can use Apple Pay, navigate through the add-to-cart process with a subscription product. Enter the View Cart page and confirm that the Buy with Apple Pay icon shows up next to the Proceed to Checkout.