This article explains how you can pay your invoice if you don't have an account or you don't want to sign in to pay it. You can do this by paying the invoice online with a credit card.
If you want to see all your invoices and manage your account you'll need to sign in. See the article How do I view my unpaid invoices?
Whenever an email is sent out to notify of an issue with payment, there is a “Pay Now” link included in that email to pay the invoice without having to sign in:
This email will also include the Company ID and Invoice Number, so you can use that for future reference.
If you need to update the credit card you have on file for this subscription, you can do so by following these steps.