You will need the Full Account permission to buy and assign seats. Assigning a seat also needs that organization in your reach, and while your account has more than one organization, changing the subscription is refused for anyone with a campus or organization limit.
While your account has one organization, add-ons work as they always have. Once it has two or more, each add-on becomes a number of seats, and each seat gives one organization that add-on.
The thing to remember is that seats are bought in one place and assigned in another. You buy them on the Billing tab, then give them to an organization by editing that organization.
For example, Riverside has Accounting with one seat. When Riverside Academy is created as a second organization, that seat stays with Riverside Community. The Academy has no books until the account buys a second Accounting seat under Billing and an admin assigns it to the Academy.
Which add-ons are seats
These add-ons are bought and assigned as seats:
App Builder
Accounting
Member Chat Pro
Remote Deposit - its seats follow enrollment, so you cannot assign them. The count is read-only.
These are not seats:
Media storage - every organization shares one storage total for the whole subscription, and an organization can also be given its own storage limit. How does media storage work across organizations? explains how sharing and limits work.
Text Messaging - an organization has texting by holding its own texting number.
Branded App - this cannot be assigned by customers. An organization with a branded app holds an App Builder seat through it.
Buy seats on the Billing tab
Go to Settings & Tools (Cog icon in the tool-bar) > Your Organization > Account Settings and open the Billing tab.
Edit your subscription. In the add-ons section, set the number of seats you need for each add-on.
Click Save.
The window reminds you of the second half of the job: A seat lets one organization use an add-on, so buy a seat for each organization that needs it. After you save, edit each organization in the Organizations list to assign its seats. How do I activate or make changes to my subscription? explains the rest of the subscription window.
Note: Seat counts only appear once your account has more than one organization, or if your subscription already carries more than one seat of an add-on.
Reducing or removing seats
While two or more organizations are active, you cannot reduce seats below the number already assigned. The window shows [count] organizations use this add-on. Remove it from an organization before reducing seats.
You can turn App Builder, Accounting or Member Chat Pro off entirely. That removes it from every organization, and with more than one organization the window warns you first: [count] organizations use this add-on. Saving removes it from all of them. Organizations with a branded app keep App Builder.
Assign seats on the organization
Go to Settings & Tools (Cog icon in the tool-bar) > Your Organization > Account Settings and open the Organizations tab.
Edit the organization that needs the add-on.
Turn on each add-on it should have, then click Save.
An organization takes one seat per add-on. Archived organizations cannot be given seats.
If the add-on cannot be turned on, every seat is already in use. The window shows Every [add-on] seat is assigned. Remove it from another organization or add seats under Billing.
When you add a second organization
While your account has one organization, that organization holds every seat and assigning is not available. When a second organization is added, the default organization keeps one seat of each add-on your subscription holds, and any extra seats stay free to assign. Remote Deposit is skipped, because it follows enrollment. The new organization starts with no add-ons. How do I add a second organization? explains the rest of that change.
When you archive an organization
An archived organization's seats stop counting, so they free up for another organization. Archiving does not lower your subscription, so change the seat count on the Billing tab if you no longer need them. How do I archive an organization? explains the rest.
What happens without a seat
Accounting - a person can open Accounting if any organization they reach holds a seat. Saving journal entries, bills or budgets to an organization without a seat is refused with [organization] has no Accounting seat. Assign one under Account Settings > Organizations. Repeating bills skip that organization.
App Builder - an organization's own app version, and its campus versions, only count while it holds a seat. Without one, its members see the base version, and the version assignment is kept for when a seat arrives. Saving an assignment for an organization without a seat is refused with [organization] has no App Builder seat. Assign one under Account Settings > Organizations.
Member Chat Pro - a chat channel gets Pro features only if every organization it is shared with holds a seat. A channel shared with All needs a seat on every active organization.
Trials
A trial covers Accounting, App Builder and Member Chat Pro on every active organization, with no seats needed. Other add-ons get no trial cover, and a trial never includes Branded App.
Chat windows that are already open pick up a trial starting or ending the next time they load.