Add licenses to a subscription paid for using a product key
You can buy more licenses for Office 365 Small Business Premium from an online retailer.
Prepaid licenses are issued to you as a 25-character alphanumeric code. After you have purchased the licenses you need, you can add them to your subscription.
To add licenses to Office 365 Small Business, Office 365 Small Business Premium, or Office 365 Midsize Business subscriptions, complete the following procedures in the order shown.
Add licenses to your subscription
Sign in with your work or school account as a global admin. Learn how to sign in.
Signing into your Office 365 subscription establishes which subscription your product key will be applied to.
Select the app launcher icon in the upper-left and choose Admin.
On the Redeem product key page, next to Want to add this to an existing subscription?, choose Sign in.
Enter your product key, and then choose Next.
If you have more than one product key, you can choose Add another product key to enter them.
On the next page, choose Next.
On the everything look right? page, choose redeem.
On the add users to Office 365 page, choose whether to create user accounts now or later, and then choose Next.
Verify that the licenses have been added to the subscription (Optional)
In the Admin center, go to the Subscriptions page, or choose Billing > Subscriptions.
If you're using Office 365 Germany, go to this Subscriptions page.
If you're using Office 365 operated by 21Vianet, go to this Subscriptions page.
Choose the subscription for which you purchased the licenses.
The number of licenses that have been purchased are listed under Licenses.