User access admins can't view portal only customers on admin hub

Issue Summary

User access admin users in centralized user management can't view or control the portal-only customers for Jira Service Management.
This is also an issue for organization admins who are not in the site-admins group for a site.

Steps to Reproduce

1. Go to admin.atlassian.com. Select your organization if you have more than one.
2. Select Products from the header.
3. Under Sites and Products, select the site that contains Jira Service Management.
4. Under the Jira Service Management section on the nav bar, select Portal customers.
   1. The portal only customers page may not be visible in the navigation panel. It can also be accessed by replacing "/access-requests" with "jira-service-management/portal-only-customers" in the page url.
5. You will see an error of: Something went wrong(We had trouble trying to fetch your customers. Refresh the page to try again.)

Expected Results

The user access admin can navigate the portal only customers page as in the steps above, and view the customer list.

Actual Results

The following error is displayed:

Workaround

The current workaround is for user access admins to reach out to org admins to check if they can be added to the site-admins group for the site.