There are 2 types of licenses that you can purchase.

First, a plan must be purchased (Start or Grow) to be eligible to purchase individual additional licenses.

Following are the two types of licenses:

1. Basic User License – By default 1 basic user licenses will be available on purchase of a Start plan. You can purchase additional licenses if required.
2. Power User License – By default 3 power user licenses will be available on purchase of a Grow plan. You can purchase additional licenses if required.

Note that currently either you can purchase Basic or Power User License based on your plan.