Mattermost Professional and Enterprise plans are offered as an annual subscription service. With your purchase you’re provided with a license key. Depending on which version of Mattermost you’re on, you may have to download and apply this license manually via the System Console.
When you upgrade to a Professional or Enterprise plan, you can enter the number of users (also referred to as “seats”) before you complete your purchase and the license key is generated. The number you enter has to be equal to or greater than your current number of activated users (formerly called active users).
You can add new users to your deployment at any time. Every quarter, during the true-up review (section 3.5 License True-up Review of Software License Agreement, also referenced in docs), we check the license license seat count relative to number of activated users. If there’s a difference, we’ll provide you with a new invoice which is payable immediately.
Please see the self-hosted subscriptions documentation for more detailed information.