Can’t add second card to 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

What is the exact error message you see on your iPhone?