Enabling Custom Number paints in iRacing graphics options
If the Trading Paints Downloader is installed and running on your computer with the iRacing sim but you suspect Custom Number paints aren't being loaded, ensure you have Hide Car Numbers checked in your iRacing graphics settings.
With the iRacing simulator open, choose Settings, navigate to the Graphics tab at the top, and under Other Cars Detail, change Hide Car Numbers to the On position. Apply the changes to enable Custom Number paints to appear next time you race.
If you change this setting, be sure to restart the iRacing sim in order for the changes to take effect.