How do you enable tap card on iPhone?

Enable Tap to Pay on iPhone

From the navigation bar at the bottom of your screen, tap = More.
Tap Settings > Account.
Select Tap to Pay on iPhone > toggle on Tap to Pay on iPhone.
Verify the correct Apple ID is shown. If not, choose Use a Different Apple ID.
Select Agree & Continue to toggle on Tap to Pay on iPhone.

Why is my debit card declining when I tap?

There are a number of issues that could result in a debit card decline. For starters, you could be mistaken about your balance, or you may have reached your daily limit for withdrawals. The bank may feel the transaction is suspicious, based on your purchase history. Technical issues may also be to blame.