As we are NASA, we are the target of a large amount of fraud. Due to that, we have very strict fraud prevention measures in place.
Most payments are declined due to a mismatch of the billing address. If the information entered into our system doesn't match exactly what the card issuer has on file, the transaction will be declined.
Most of the PayPal payments that get declined are due to the customers bank not willing to accept the transaction. In this instance, our system recommends you contact PayPal for more information.