Once you have a primary account for G Suite created and active, you can increase the number of seats in your G Suite subscription.
- Login to your account and go to the Websites, Email & Security tab.
- Click on the G Suite product in the list, or use the Actions button.
- Click the Upgrade button.
- Choose the desired number of users you'd like to upgrade to and click Continue.
The system will then calculate the payment necessary for the new users, and to extend your current users to match the expiration date of your new account(s).
Complete the checkout process.
The system will automatically increase the number of allowed seats for your subscription, you can proceed to create your new users at https://admin.google.com