When filing a flight plan in Sim Brief and I choose the Fenix A320, GSX will not recognize the Aircraft. Saying this is not a MSFS Aircraft. The Fenix Aircraft is not included in Sim Brief.
What do I have to do, when selecting the Fenix?
You could try downloading and using a Fenix A320 SimBrief airframe profile from Simbrief Airframe for Fenix A320? - General Discussion - Microsoft Flight Simulator Forums
If GSX still has a problem, you might like to ask in their forum.
Cheers
Ian