We’re aware of a bug with the coupon that’s been introduced on launcher. On launcher, if you have the coupon, you will get an error if you click on the shopping cart. You’ll see the message “Your Shopping Cart is Empty,” even when you have items. That means you’ll be blocked from completing the checkout process on launcher. The only way to solve this right now is to go to the Marketplace website and complete the checkout process there.
We’ve reported the bug, and we’re asking our engineers to solve this as quickly as possible.
Sorry for the inconvenience, we’ll update this thread when resolved.