In case you did not permit iFlicks to add videos to TV app / iTunes on the first request, macOS prevents iFlicks from asking and silently disallows this process. iFlicks detects this and shows a message like:
TV app does not allow iFlicks to add files because access to TV app was denied by the user.
iTunes does not allow iFlicks to add files because access to iTunes was denied by the user.
In order to solve this, you need to go into System Preferences -> Security & Privacy -> Privacy -> Automation and tick the checkmark in front of iFlicks.