I am having this same problem also. Tried everything and read many questions and answers about it. My Lua files do not appear in the option "control sent when button pressed"... I uninstalled and reinstalled fsuipc6 three times with all the default options. Used <C:\users\XXXXX\Documents\Prepar3d V5 Add-ons\FSUIPC6> for installation, put my .lua file there toghether with FSUIPC6.ini, FSUIPC.dll, installFSUIPC6.log etc.
Please help !! What could be wrong ?
Read all manuals with attention and going crazy with this. The only strange thing that happens is the option for Prepar3d 4 appears, when I don´t have it installed, but I unchecked the option.
I include my installation log here. Do I need to change something in the installation ?