Hi
There has been a discussion on this point here Devialet: Transport: Device in Use.
In summary you need to ensure that the CI firmware update (factory Config) is done (without SD config card) - you will know if the firmware has been uploaded correctly by pinging the IP address in your PC. If the Devialet in your network (with the IP address) is showing a message stating “configuring”, then CI firmware has not been properly installed but may still appear in your network but Roon will not recognise it as an endpoint. You then need to reset the latest firmware (factory config) - once you see the screen (noted in the above discussion) on your PC/ Mac - then also reboot Roon server and you will should find it appearing as an endpoint in Roon (with the Devialet expert icon).
If you are using wifi you will need make sure you have the settings configured both in Roon Core and Devialet - with wifi I cannot emphasise enough that you have a robust router (and also if possible you should dedicate a channel just for audio that is separate to video and other devices). My preference is ethernet, I have used a switch box and rely on ethernet and so far have had no problems other than what is noted jn the above post and acknowledged by Devialet as bugs.
Good Luck and I hope you get it working!