Occasionally this can occur when entering your address on iOS, and revolves around a requirement of Apple Pay.
Following these steps should help get things working for you:
- Update Shipping Address also includes having a valid phone number and email associated with the card's billing address. Using the same methods provided earlier, ensure that an email and a phone number are provided as part of your shipping information
- Try removing the card from your Apple Wallet and re-adding it
- Use a two-letter code for State. For example, use CA, not California
- Spell out all other abbreviations. For example, use South
- Spell out the country or region name. For example, use United States, not U.S. or US
- Enter a ten-digit phone number with no special characters such as +, -, (, or )
If these steps don't help, unfortunately you may need to reach out to Apple support, as the issue is technically on their end.