Q: Sling tv wont log into apple tv 4

You can check for current connection problems here >  http://downdetector.com/status/sling

I'm sorry to hear that. However, it's a problem within their app. As a first step, try force quitting the app, then run it again. You could also try deleting and reinstalling the app, in case that clears it up. This is just a user forum here, so we can't help much, unless another Sling user knows the trick.