This is going to sound obvious, but make sure you entered your credit card information correctly.
- Double check your entry.
- Make sure your billing zip code matches your card.
- Check your bank account to be there are sufficient funds. (Is payday tomorrow, not today? We get ahead of ourselves thinking it's Friday all the time.)
- If you're based out of the country, make sure your credit card company is aware you're making a purchase in the United States.
- If everything seems to check out on your end, call your bank to be sure your card is in active status.