is it possible to add a mileage counter that shows how many miles a vehicle has already driven?
Yes, this is possible
The system has been updated. There was a bug on the map, it has been fixed and now you are notified when the update comes.
there’s no stress 
New version is out and available in the new version 
DO NOT BUY ANYTHING FROM THESE GUYS…
They have built a bad reputation around the fivem community ripping people off. Honestly, I didn’t believe it but the very first script I bought from them I seen exactly what everyone was talking about.