If you're using Airplay to share your screen and your iOS device cannot discover the Montage receiver, go to Settings – Network & Connections, ensuring Airplay Receiver is switched to On.
If using Montage on a Windows receiver, you will need to ensure the Bonjour service is running. You can check this by typing Services.msc into the search bar on your Windows taskbar.
In the new window, Bonjour should be listed, and status should state Running. If Bonjour is not listed, you will need to install it.
Users should also confirm Bonjour services are allowed across the network, including ports TCP 4700, 7000, 7100
Download link - Download Bonjour Print Services for Windows v2.0.2 (apple.com).
Pressing New session will reset the connection.