The trailer modules are not coded to the car but do need a software update to recognise them - until the software is loaded, nothing usually works. This means you have to go to a dealer or a good indie will licenses VIDA. Whilst VIDA might see the TRM as it's on the canbus, the CEM needs software to talk to it.
You can buy generic trailer modules that don't need programming or software but they won't have all of the functions such as bulb failure warning, parking sensor defeat or fog light control. Most towbar outlets will sell them. Or you could just buy a relay and splice into the wires - will work just as well....
https://www.pfjones.co.uk/volvo-v50-...9260500pf.html