I am unable to add debit or credit card on my Apple Wallet

That’s not an error message or notification that pops up. But that’s OK. When you see that, the region for your iPhone or Apple ID or both are set incorrectly. Another possibility is the bank that issued the card doesn’t support the region or country you’re in, if you’re currently traveling.

Confirm your region is set correctly.

Change the language and region on iPhone - Apple Support

Change your Apple ID country or region

If you can't add a card to Apple Wallet to use with Apple Pay - Apple Support

Regards.

what is the error message you’re receiving? Have you agreed to the terms and conditions?

What is the exact error message you receive when trying to add a card? Why are you trying to update information? You do not update and cannot update information on cards in your Wallet app.

What app are you in, Settings or Wallet? You can’t update information in Wallet app. The issuing bank updates information such as expiration date as needed. It sounds like your in Settings > Apple ID.

Wallet app looks like this,

What app are you in?