Login to the Magento 2 admin panel and go to Stores > Configuration > Sales > Payment Methods. Scroll down to the Subscribe Pro | Apple Pay section and expand it.
- Turn on the "Enabled" setting (and optionally the "Allow Non-Subscription Transactions" setting) and click the Save Config button.
On an Apple device that can use Apple Pay, navigate through the add-to-cart process with a subscription product. View the Cart page and confirm that the Apple Pay button shows up below the Proceed to Checkout button.
Apple Pay should now be fully functional on your Magento 2 website.