A paid seat is applied to a profile once you submit an answer from said profile. That profile will then show it has an Active Seat associated with it, which can be viewed on your Profiles page: https://featured.com/admins/profiles.
To apply your paid seat, from the Questions page, click Answer for a query you'd like to respond to. At the top of the pop-up, there should be a button with two arrows. You can use that button to pick between your profiles. Select the profile you want to use, type your response, and submit.
