Unable to add a card to Apple Wallet

There are several possible reasons you might be experiencing issues. So let’s start with a few basic steps. I’ve added links to support articles that may offer solutions to issues you might encounter. 

Are you in a country or region that supports Apple Pay?

Countries and regions that support Apple Pay - Apple Support

Does your financial institution support Apple Pay?

Apple Pay participating banks in Asia/Pacific, Africa, Europe Latin America, Middle East and United States - Apple Support

Confirm your region is set correctly.

Change the language and region on iPhone - Apple Support

Change your Apple ID country or region

I met the same issue recently.

1) Please check if your card is not locked.

2) Follow the instructions from the following KB:If you can't add a card to Apple Wallet to use with Apple Pay - Apple Support

3) I met the same issue when I migrated my old phone to the new phone. I use the quick start for the data migration, however, it didn't processed the Apple Pay info correctly. But after several weeks, i tried again, it works afterwards.