Samung Pay Beta (USA)

I registered for the Samsung Pay Beta program yesterday. Today I received a mail that I've been accepted in the Beta Program. I happily started the Samsung Pay app and it showed a new screen for installation. I installed it. The interface looks good. You can just scan the card and it captures the card number and expiry date automatically. Rest of the information has to be filled manually. However, It didn't accept my CHASE or AMEX card. It gives following error:-

Registration failed
Unable to register your card. Try another
card or contact the card issuer. (645101)

Anybody else having similar issue ?