If you're using Apple Pay on your iPhone or iPad, you may have already realized that you can add multiple cards that you can toggle between when making purchases. Even better yet, for times when you don't want to launch Passbook at all, or just to make the process even quicker, you can choose a default payment card. That means unless you manually choose a different card for a specific transaction, the default will be used for every transaction you make, both online and in-store.
How to choose a default credit card for use with Apple Pay
Launch the Settings app on your iPhone or iPad that's compatible with Apple Pay.
Tap on Passbook & Apple Pay.
Tap on Default Card.
Tap on the card you want to use as your default.
That's it! Unless you manually change the card you're using when making a purchase, the selected card will always be used.