During the purchasing process you are receiving the error message: 
 You have already signed up with this account.

This message is displayed if a PayPal account, that is linked to the credit card you are using, already exists. You will need to login to the PayPal account associated with this credit card or use another credit card not linked to a PayPal account to proceed with the order.

Alternatively, you can give us a call (415-507-1623) and we will be happy to process your credit card over the phone.