If you are running RealDash on same computer with the game, see this post first:
Localhost connections on Windows 10/11 - General / Bugs and troubleshooting - RealDash Forum
- Make sure you are on the same network as your computer or console.
- Go to game setting menu (top-right corner from main menu) “Options & Help” → “Gameplay” and set UPD to 1.
- After setting the correct source in RealDash the game should send you car data when the race starts.