Metal cards require more precision to be tapped due to the material they’re made out of. NFC communications can’t pass through metal. Here are some tips for a successful tap.
To tap the card on iPhones:
Have the QR code facing the phone. Tap the QR code on the top back edge of the phone. Place the QR code where you can still see part of it going over the phone. Make sure the phone is unlocked.
To tap the card on Androids:
Have the QR code facing the phone. Tap the QR code on the back of the phone either on the center or the top of it. Make sure the phone is unlocked. Hold it there for 2-3 seconds.