You will not be able to place an order (checkout) if you are not logged in. Please log in using your registered email address. If you’ve registered with your company-associated email, it will be used to automatically add you to the company. You can also log in using a personal email to place a personal order.
There is a known bug where it appears you are logged in, but checkout is unavailable. Until this has been resolved, you can log out and then log back in to fix this issue.