The extension recently stopped populating search results for both Radarr and Sonarr. I solved this by going to Settings then Advanced and pressing the green button "Auto populate from API" - this will change the setting to "Prevent auto populate".
Next, in the box for "Search path URL" type: /add/new?term=
Apologies for this, it was caused by attempting to limit the URL permissions required by the extension. I'm pushing a new release (v2.8.1) now, so this should be fixed very soon.
