Need some help with Add-On Vehicles

Hello everybody!

I used the tutorial for Add-On vehicles ([How-To] Add-on Vehicles (Detailed))

And I did everything step by step: except for the handling files because I dont have these.
So my vehicle is working when I give it the name of a real GTAV vehicle but it isn’t working if I call it something else. How to fix this? Because I want firetruk2, firetruk3 etc.

you can’t do that!