why i cant add my card 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

Provided you meet all of the criteria above...

Contact Support at your bank and ask them to check how many 'tokens' you have active on the card in question, and explain the issue you're experiencing. Each card will have a finite amount of tokens that can be used for activations across various sites & platforms, and they can be duplicated quite easily, I.E. if you shop at Amazon they will require only one token but there may be 3 or 4 currently active.

Your bank will be able to clear down any duplicates which should then free up tokens and allow you to add your card to Apple Wallet.