Below are the steps to add a card to your iPhone Apple Pay:
1. On your iPhone, open Wallet.
2. Tap Add Credit or Debit Card.
3. If you have a supported credit or debit card on file with iTunes, enter the card’s security code. Otherwise, use the camera to capture the information on your credit, debit, or store card. Then fill in any additional information needed, including the card security code.
4. Tap Next. Your bank will verify your information and decide if you can add your card to Apple Pay. If they need more information, they'll ask you to provide additional verification. You can verify your card any time after you add it. Just return to Wallet on iPhone and follow the next step.
5. Once your card is verified, tap Next. Then you can start using Apple Pay.