Pager on Windows is currently in beta. There are still bugs with Windows 10 in particular, because of the new windowing system.
Suggestions for things to try if you're unable to get it working:
1. If you're using Pager with ProPresenter, are you on SDI? The app can only support VGA, DVI, or HDMI - we must be able to display a "window" over top of ProPresenter. SDI connections are controlled by ProPresenter, and we don't have the ability to add anything to that image or control it.
2. On ProPresenter, also ensure "Display as topmost layer" in the app's settings is disabled. See this article for details.
3. Test with only a single monitor connected, or only one second display connected to Windows. If you're able to drag windows to that extended display, relaunch Pager and send a test message again.
4. Do you have a working Internet connection? Ensure the connection is live, and Websockets ports (443) are unblocked in your firewall.