On the left menu, click on Devices > Chrome > Devices.
Here, click on Upgrades at the top.
On the prompt, you will see the amount of licenses available under Unassigned.
If the number is 0, you need to purchase Chrome Upgrades. To purchase new Chrome Upgrades follow the steps on this Help Center article, keep in mind Google Workspace for Education and for Nonprofits can only purchase them from a reseller.
Cause
The system will evaluate the available licenses for the domain that the account belongs to first.