Pro Sites "pro-site-5/?bid=" Page Not Found during Checkout

I did the settings but the checkout page seems to be missing.

"Checkout Page There was a problem finding the Checkout Page. It will be created when you save the settings on this page."

I saved the settings numerous times, just doesn't work.

"You have 7 days left in your Pro free trial. Checkout now to prevent losing Pro features »" when I click on it, it goes to, which says "Error 404 - Page not found"