Purchase Buttons Going to Empty Cart

I just started having a bug where when I click the purchase button for my products, they go to the checkout page, but I see the message that says “Your cart is empty.”

This only started happening after I migrated the latest version of my site to the online location. Its working fine in MAMP, and was working fine online until I migrated the changes, which were just some little updates to my theme and database.

How can I get the purchase buttons working again?

The page I need help with: [log in to see the link]