If you get to Shipping & Payment (where you choose Credit Card or PayPal), then the Confirm page, but then get kicked back to the "Your cart has been changed. Unfortunately 1 or more items in your cart is sold out." message then just rinse/repeat. But if you get to a page with a 3 min timer to...
I used my Chase Southwest Rapid Rewards Visa credit card. I had to call my card company and have them stay on the line while I checked out because it kept getting declined