The free plan used to include one Permit Advisor run, ever. It now includes 3 runs in any 24 hours. Run it when you create your project, then again from the project page after you add a description or change the location. It leaves out permits the project already has, so a second run only adds what's new.
As before, a run that finds no permits for your project, or can't finish because Permit Advisor is unavailable, usually doesn't count. Pro still includes unlimited runs, along with unlimited projects, client dashboards and the calendar feed.