Almost every time this happens, it's a case where the billing address you have entered for your Paizo account doesn't exactly match the billing address on record at your back or card issuer. Paizo's anti-fraud software is very picky. Check the address on record at your bank and enter it at Paizo exactly the same way.
If that doesn't help, do not continue to post in this thread. Customer Service works from the bottom of the list to the top so "bumping" the thread with new information will move your issue to the back of the queue. If it's anything other than the address-verification issue, a Paizo Customer Service staffer will have to help you with it. Unfortunately, they are running behind right now because of working from home during the pandemic.