How to configure Remote Desktop settings for multiple monitors?

I’m trying to enable spanning across three monitors in Remote Desktop. The check‑box “Use all my monitors for the remote session” is greyed out. Any ideas?

Make sure you’re using the latest Remote Desktop client (mstsc.exe) and that the remote Windows edition supports multiple monitors (Professional or Enterprise). Also, the remote machine must be using at least Windows 8/Server 2012.

If you’re on a corporate network, the RDP gateway might be limiting features. Ask your admin to verify the RDP‑TLS policy allows “Maximum Display” set to 2 or more.