I can’t verify my card on Apple Pay and I don’t know why?

Change, add, or remove Apple ID payment methods - Apple Support

If you can't add cards to Wallet for Apple Pay - Apple Support

Apple Pay Cash - Official Apple Support

Set up Apple Pay on your iPhone, iPad, or Apple Watch

Is the phone number you are using able to receive an SMS text message? If not, then that is why you are not getting the message.

Contacting Apple Customer and Support Service

1. Apple Store Customer Service at 1-800-676-2775 or visit online Help for more information.
2. Primary support help at Contact Support.
3. To contact product and tech support:  Contacting Apple for support and service including international calling numbers.
4. For Mac App Store: Apple - Support - Mac App Store.
5. For iTunes: Apple - Support - iTunes.