Not able to add credit card in wallet

Make sure the iPhone is set ti a country where Apple Pay is available in Settings->General->Language & Region->Region

Link-> Countries and regions that support Apple Pay - Apple Support

If it is correctly set, then explain what happens when you try.

I've had the same issue. I contacted my credit card provider but they were less than helpful. Apple customer service was much more helpful - 1-800-MY-APPLE. There are a lot of external sites offering suggestions, but I don't believe we can link to them here.

I'll be curious what the community offers as suggestions. I hate contacting my card issuer!