You mean on Kickstarter, right?
Make sure that your card is of the accepted type, from Kickstarter Help:
You can use a debit or credit card associated with Visa, Discover,
JCB, MasterCard, or American Express. Discover and JCB cards are
currently only accepted for US-based projects.
We do not currently accept Maestro or Visa Electron cards. If using a pre-paid credit card,
please make sure that the card has a value of at least $1 more than
your pledge amount.
Validation is immediate, as the charge get pushed directly when you try the "Fix payment" function.
Also make sure with your bank that your cards are open for online and over boarder purchases, as most banks have automatic fraud protections against that.
Edit: Hah I were to slow. Matthew already gave you all the answeres