This function returns the name (as a string) of the currently selected configuration for your game. For more information on configurations please see the section Configurations.
os_get_config()
if (os_get_config() = "Free_Version")
{
global.Ads = true;
}
else global.Ads = false;
The above code will check to see which configuration is being used and if it is the one called "Free_Version", ads will be enabled in the game.