Buy another Office 365 for business subscription
If you already have an Office 365 for business subscription and you want to buy another subscription for your organization, the best way is to do it is through the Admin center. If you haven't yet purchased the first Office 365 for business subscription for your organization, go here to select a plan.
When you buy another subscription through the Admin center, you're guaranteed that the new subscription will be associated with the same organization (domain name space) as your existing subscription. This makes it easier to move users within your organization between subscriptions or assign them a user license for the additional subscription they need.
After purchasing a new subscription, you'll need to assign the users who you want to use that subscription a user license for it. To learn how, see Assign licenses to users in Office 365 for business.
Buy another subscription
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.
On the Subscription page, choose Add subscriptions.
You'll see the subscriptions that are available to your organization. Any subscriptions that you've already purchased are identified like this.
Mouse over or tap the subscription that you want to buy, and then choose Buy Now.
Enter the number of user licenses you need, chose whether to pay each month or for the whole year, and then choose Add to Cart.
Your cart opens. If your cart disappears from the screen, select Cart to reopen it, review the order and then choose Check Out.
Review the pricing information and choose Next.
Provide your payment information, and then choose Place order.
On the confirmation page, choose Continue.