We've confirmed that this issue is resolved. You can complete purchases for Articulate 360 subscriptions and seat adds.
Posted Dec 11, 2019 - 16:31 UTC
We're investigating an issue that is preventing tax from being properly calculated on Articulate 360 purchases, including adding seats to an existing subscription. As a result, you may not be able to complete your purchase. We'll let you know as soon as we have more info. We're sorry for any trouble!