The MakeCall is the PBX setting up the call. When you answer the MakeCall on your mobile app you will hear the MOH until the other end of the call answers.
If you want to use the Windows 3CX app to make/receive calls you need to put the app in to softphone mode. This is the icon in the top left. If it's using the deskphone it will look like a deskphone and if you click it again it will use the softphone. Ignore the call made to your mobile app, it's only calling that because it's online and registered too.