If you've migrated from the App Store version to the Trial version, you may have issues installing the HelperTool.

The solution is to first use the AppStoreHelperTool to uninstall the AppStoreHelper:
https://sweetpproductions.com/products/wifispoof4/WiFiSpoofAppStoreHelper.dmg

Then restart the Trial version of WiFiSpoof and the HelperTool should now install