I have a dedicated folder called "swift custom sounds" where all my custom notification sound files are stored. As suggested by you, one of them is called unicommessage.wav. I added the same file to both swift-0.12-32bit\share\sounds and my custom path.
On the "Audio" page I successfully tested the notification sound by selecting and deselecting UNICOM message notifications. But when connected to VATSIM, no sound is played when other players send messages on UNICOM 122.800.
swift 0.12.35 - 32bit FS9
I have a dedicated folder called "swift custom sounds" where all my custom notification sound files are stored. As suggested by you, one of them is called unicommessage.wav. I added the same file to both swift-0.12-32bit\share\sounds and my custom path. On the "Audio" page I successfully tested the notification sound by selecting and deselecting UNICOM message notifications. But when connected to VATSIM, no sound is played when other players send messages on UNICOM 122.800.