Downloading movies with Showbox requires the latest update APK release. This is not available for download at this time. If you already have it, you should NOT use it without your Surfshark VPN app connected first. Corporate and government agencies are actively targeting Showbox users lately, so the developers have gone underground, and the APK is currently unavailable.
Seriously, use a Showbox alternative such as Cinema HD if you want to download and stream free movies and TV shows, but only through an encrypted connection.