def ensure_app_exists!
      return if Spaceship::App.find(Sigh.config[:app_identifier], mac: Sigh.config[:platform].to_s == 'macos')
      print_produce_command(Sigh.config)
      UI.user_error!("Could not find App with App Identifier '#{Sigh.config[:app_identifier]}'")
    end
def ensure_app_exists!
      return if Spaceship::App.find(Sigh.config[:app_identifier], mac: Sigh.config[:platform].to_s == 'macos')
      print_produce_command(Sigh.config)
      UI.user_error!("Could not find App with App Identifier '#{Sigh.config[:app_identifier]}'")
    end
Makes sure the current App ID exists. If not, it will show an appropriate error message