You can add your virtual card or your debit card to your Apple wallet by following these steps:
1. Open the wallet app in your iPhone
2. Hit the plus sign in the upper right hand corner
3. Click "Debit or Credit Card" and hit continue
4. If you're adding your debit card to your wallet, you'll be able to take a picture of the card. If you're adding your virtual card, you'll need to hit "Enter Card Details Manually."
5. Follow the prompts to finish adding your card. You can find your virtual card details in the Spending tab of the Milli app under "Cards." Swipe to see your virtual card and click on "Virtual card details."