The known cases and solution.
Technical support:

FM Network UDP connection issue on Windows PC/Laptop
– Please disable firewall, and enable auto network discovery on your Windows System Settings

FM WebSocket connection issue on non-local applications
– In FMSocketIOManager settings, please make sure your IP address is same as your node.js server
– If you are hosting it on your own machine, you should enable port-forwarding for public network connection
– If you are hosting on cloud, please make sure your IP & Port are reachable.

FM Desktop Stream issue: [FMD] 0:\\.\DISPLAY1 => Unsupported
below is suggested answer by parkerhg in forum posts #513
make sure Windows 10 uses a specific GPU when running your application.
You can do this through windows or your GPU, but depending on how you do it windows sometimes overrides your choice.

I found this stack overflow thread and some of the links on it to be very helpful:

But I’ll summarize what worked for me here as well:
basically, if you go to control panel -> System and Security -> System -> Display -> Graphics settings, you can set a program (like Unity) to use a specific GPU through windows (you’ll have to restart the program for it to work though)

Duplicated websocket-sharp.dll with PUN2 or other plugins
– Removing one of the websocket-sharp.dll should solve the issue
– or removing the FMWebSocket folder completely with ease