User licensing in Advanced Portal Reports app happens exactly the same way as in any other app on Atlassian marketplace.
This implies that:
app licensing applies to licensed Jira users only.
app licensing is aligned with Jira Core or Jira Software license (depending on which one has more users).
in full accordance with Atlassian Marketplace rules, app licensing DOES NOT apply to your Jira Service Desk agents.
If you have the following cloud/server instance:
Jira Software with 56 users
Jira Core with 10 users
Jira Service Management with 22 agents and 99876 Service Desk customers (who do not have access to Jira, or include the 56 software users or 10 core users).
You will need to acquire 56 user licenses for Advanced Portal Reports for Service Desk.
You can also check your bill estimate to be completely sure about the price you are going to pay. In order to do that go to the Billing section of the administration:
And then check your bill estimate for our Advanced Portal Reports.