If you signed up for STARZ through Sling TV, you would not have access to the STARZ app. To watch STARZ with your Sling TV login credentials, you need the Sling TV app.
If you signed up for STARZ through Sling TV, you would not have access to the STARZ app. To watch STARZ with your Sling TV login credentials, you need the Sling TV app.