GSX uses the standard Simconnect notification bar, and we don't have any control over it so, if it doesn't appear with FlyInside, your only option is to report it to the author, because it's surely something he would like to support, since it's the most official way of displaying messages in FSX/P3D
FSUIPC options don't have any effect on it, because we don't use FSUIPC, just plain and standard Simconnect.