License Inquiry: Purchasing JIRA Zephyr Scale for Specific Project Users

If any organization has 50 users on JIRA for managing multiple projects. And if they are interested in purchasing zephyr scale for particular project but they only require licenses for only 10 users within that project. Will they required to pay for licenses for all 50 users, or is there a way to only pay for the 10 users who will use JIRA Zephyr scale?