racing app not work?

You mean the 'Hotlapping' app?

What doesn't work exactly?

 

But which app are you trying to use exactly? There is no app specifically called 'Racing'.
There are apps like 'Racing Position', 'Timer' and etc, but those are not meant to be used in free-roam.
Those will be used automatically only in scenarios/quickraces.

If you want to race in free-roam, you got to use the 'Hotlapping' app, to first create the course, and then race around it and time yourself.

 

No, those apps are only for scenarios/quickraces, not meant for free-roam usage.

The 'Hotlapping' app is what you want to use.

1. First add that app to your screen:
2. Click 'Start Hotlapping' to first your first checkpoint:
3. The button will now turn into 'Add Checkpoint'. Basically like this you create your own course:
4. As soon you drive back inside the first checkpoint, the 'creation' mode will end, and the game will start to time you.
5. You can now race against the timer

If you want, you can save your course by clicking the dedicated button:


Next time you load the map, just click the 'Icon' folder to load a 'pre-made' course available for that map.