You may need another card to complete the transaction. Apple Card is a prepaid virtual debit card and it displays virtual card number (Apple Pay number is different), expiration date and CVV security code. The merchant may be attempting to verify the balance on the card and determine if the charge will go through. Card verification usually requires the cardholders name. The name on your card would be the name you verified with Green Dot Bank. If you haven’t verified your identity yet, your card is probably failing verification.
Identity verification for Apple Card or Apple Cash - Apple Support
https://applecash.greendot.com/termsconditions/