One of my subscribers brought this to my attention and there doesn’t appear to be any sales currently in forza horizon 3 even though part of the forzathon is 30% off everything in the autoshow
this has not been posted about enough yet
check the main Forzathon thread just before yours
and apparently it is now working, try restarting your game
First resort is always Reboot your device.
Use the main Forzathon thread for further discussion.