Am unable to add my cards in apple pay

Your card might not support Apple Pay. Here’s a list of all the banks that currently support Apple Pay: Apple Pay participating banks in Canada, Latin America, and the United States - Apple Support

If your bank is on the list, you can add that card to Apple Pay.

Why not?

What happens when you try?

Do you get an error? If so, what does it say?

If you get the Learn More popup, that takes you to the support document you posted from when tapping on the (➕) icon, then make sure your iPhone is set to a country or region where Apple Pay is supported in Settings➜General➜Language & Region➜Region.

click here ➜ Countries and regions that support Apple Pay - Apple Support

As Philo124 suggested, go to Settings>General>Language & Region>Region. I would add further advice: Regardless of what it says, even if it appears to be correct, reselect the correct region.