I had the same issue the first time. I did a remote chat to Samsung from inside this forum. there is a support option in here. they were able to remotely connect to my phone and pushed an update to the galaxy apps. I was then able to add all cards right away!! for some reason the update to the apps doesn't push out automatically sometimes!
Go to 'Galaxy App Store' and search for 'Samsung Pay'. See if there's any update available. If there is, update and try again. If no update is available, contact them through Live Chat and they'll find the problem and guide you.