If it’s in Personal Devices, it can’t be assigned to a room. You need to add it as a ST device by doing Add Device-> Select by Brand-> Samsung->TV, assuming your TV is a supported model.
So i tried both ways and both doesn’t work. When i go on the site , it doesnt pick up any device at all.
With the other way , i have a samsung 5 series N5300 smart tv which is supported, it shows on the app as being supported too. If i scan and do that process when it picks the tv up it automatically says “it will be directly connected to phone” and below it says “can’t assign to room” thats with only pressing add then selecting device.
To be fair the device spec does indicate full ST integration but the images on tbe web site are outdated so it could be it used to work before Edge transition or a geographical lock out.
Phone and Tv both on same network 2.4ghz not 5ghz which might work but best to stick to 2.4ghz to begin with or is it hard wired to your Lan ?
If its Lan make sure cable is good and router not blocking anything