Unfortunately, sometimes the app closes for unknown reasons. Here are a few things you can do to get it working again:
Note: If you're experiencing this issue on an iOS device, make sure your Sling TV app is up to date and running app version 188.8.131.5276. You can find which version you're using by selecting Settings then Support in the Sling app.
Click here for details on updating the Sling app on your device.