There are a variety of reasons that your card could be declining. The most common cause could be that the card's billing zip code is different from the zip code for your address. If so, you need to enter that zip code in the space provided on the form:
If you are confident the zip code is correct and there are sufficient funds on the card, please feel free to reach out to our help center at 916-790-6150 for more insight into the reason for the decline.