I am unable to use the app because the get started button is not active (doesn't work)
I'm sorry you are having trouble. That is typically caused by a momentarily bad network connection. If you force-quit the app and relaunch it, the issue should be resolved. Again, sorry.
Please sign out, then uninstall and reinstall the XFINITY Stream app and retest.
Please let us know if you tried that and the issue persists.