Unable to edit payment info "Apple ID account"

[Boutrosn]

I'm trying to buy Whatapp Messenger through the App store. Whenever I try to add the credit card information i get this error
"Your payment method was declined. Please enter valid payment method information"

What should I do to fix it ?

 

[McGiord]

If you are in a Mac, enable the cookies in Safari, the iTunes Store needs them for running payments.
Or you CC doesn't have enough funds to authorize it, or it is void? get the new one in the mail?